Publications
| Title | Abstract | Year(sorted ascending) Filter | PMID Filter |
|---|
| amino acid sequence microheterogeneities of basic (type ii) cytokeratins of xenopus laevis epidermis and evolutionary conservativity of helical and non-helical domains. | three clones coding for carboxy-terminal portions of type ii cytokeratins have been isolated from a cdna library constructed from the epidermis of the frog xenopus laevis. these clones have been identified by hybridization-selection-translation and northern blot analysis, and contain sequences complementary to mrnas of similar size that code for three different polypeptides of the mr 64,000 group, ia-c, i.e. the only major type ii cytokeratins expressed in this tissue. a comparison of the corres ... | 1985 | 2413219 |
| establishment and characterization of a permanent t-cell line producing an antigen non-specific suppressor factor. | a permanent cell line designated sl4c has been established from a primary culture of murine balb/c spleen cells regularly stimulated with large doses of irradiated allogeneic cells plus exogenous interleukin-2(il-2). after 8 months of cultivation, the cells of the sl4c line proliferate spontaneously and do not respond with an increase in proliferation to alloantigenic stimulation. the cells have the lyt 1.2+, lyt 2.2-, l3t4a+, thy 1.2+ phenotype and exert a strong suppressive effect upon stimula ... | 1985 | 2414213 |
| role of calcium mobilization in mediation of acetylcholine-evoked chloride currents in xenopus laevis oocytes. | the involvement of ca ions in the mediation of muscarinic cl- current responses in xenopus oocytes was studied using the voltage-clamp technique and direct measurements of 45ca efflux. the injection of ca into the oocytes produced a dose-dependent transient inward (depolarizing) current carried by cl. this current was occasionally followed by a second, long-lasting inward current. the muscarinic response was evoked by the application of acetylcholine (ach). it consisted of a transient inward cur ... | 1985 | 2414433 |
| sodium conductance and the activation potential in xenopus laevis eggs. | experiments have been performed to identify the membrane permeability changes causing activation potential in xenopus eggs. the eggs were artificially activated either by pricking or by addition of the ca2+ ionophore a23187 to the bath. two different ionic currents appear to control the activation potential: (i) a chloride current which develops after a delay of 30 s to 5 min from the activating stimulus and which, in low external chloride, produces a depolarization and, (ii) a voltage-dependent ... | 1985 | 2414723 |
| the effect of crown ethers on ionic currents in myelinated nerve fibres from xenopus laevis. | the effect of several crown ethers on the currents at the node of ranvier was studied. at differing potencies they caused a time- and potential-dependent inactivation of potassium permeability and a time- and potential-independent decrease in sodium permeability. the relative effect on potassium and sodium systems varied and was not directly related to their ionophoric properties. a computer analysis indicated that the induced inactivation was dependent on the normal potassium activation mechani ... | 1985 | 2414973 |
| mediation of anion transport in oocytes of xenopus laevis by biosynthetically inserted band 3 protein from mouse spleen erythroid cells. | mrna from the spleens of anemic mice was purified by oligo(dt)-cellulose chromatography and fractionated by density gradient centrifugation. after injection into oocytes of xenopus laevis, two of the four fractions obtained led, after 16 h of incubation at 20 degrees c, to the expression of mouse band 3 protein, as demonstrated by immunoprecipitation with polyclonal antibodies against mouse band 3. flux measurements showed an approximately 2- to 4-fold increment of 36cl- uptake, which could be a ... | 1985 | 2415354 |
| cmp-sialic acid, the sole sialosyl donor, is intra-axonally transported. | n-acetyl-d-[6-3h]mannosamine was injected into the 9th dorsal root ganglion of xenopus laevis and the intra-axonal transport of chloroform/methanol-soluble radioactivity was analyzed using thin-layer chromatography coupled with fluorography. three radioactive groups were distinct in consecutive segments of the sciatic nerve. the first is due to n-acetyl-d-mannosamine itself which labels the nerve uniformly, but does not seem to migrate within axons. the second group, representing most probably c ... | 1985 | 2415391 |
| molecular cloning of cdna coding for human preprourokinase. | a cdna library was constructed in pbr322 from 18s to 20s mrna that was extracted from human kidney cells, fractionated on oligo(dt)-cellulose column and sucrose-density gradient, and confirmed for urokinase production in xenopus laevis oocytes. the escherichia coli rr1 transformants were hybridized to synthetic oligonucleotide probe prepared according to the known amino acid sequence, glu 73 to glu 77 of human urinary urokinase chain b. the entire cloned cdna covers a 2250-bp region, wherein the ... | 1985 | 2415429 |
| nucleotide sequence of a xenopus laevis mitochondrial dna fragment containing the d-loop, flanking trna genes and the apocytochrome b gene. | extensive corrections of the nucleotide sequence of the xenopus laevis mitochondrial (mt) displacement (d) loop and surrounding genes [wong et al., nucl. acids res. 11 (1983) 4977-4995] are reported, including addition of two stretches of nucleotides and 60 scattered modifications. the additional sequences presented here correspond to the apocytochrome b gene, the trnaglu gene and part of urf6. this allows us to propose a conformational model for the x. laevis apocytochrome b protein and also pe ... | 1985 | 2415430 |
| ultrastructural localization of rrna in hela cells, rat liver cells and xenopus laevis oocytes by means of the monoclonal antibody--protein a--gold technique. | the postembedding localization of rrna was investigated in ultrathin sections of hela cells, rat liver and xenopus laevis oocytes by means of the monoclonal antibody to rrna and protein a-gold technique. the incidence of gold particles was highest in nucleoli and cytoplasmic areas containing ribosomes. the chromosomes were labelled less than the surrounding cytoplasm in mitotic hela cells. in nucleoli of hela cells and rat hepatocytes, the labelling of areas containing ribonucleoprotein componen ... | 1985 | 2415490 |
| mobilization of specific maternal rna species into polysomes after fertilization in xenopus laevis. | unfertilized eggs of many species contain large amounts of maternal mrna that are used to support protein synthesis during the first few hours of development, before the onset of embryonic transcription. we have examined the accumulation of nonpolysomal maternal rnas in polysomes after fertilization in xenopus laevis by measuring the distributions of specific sequences in nonpolysomal and polysomal fractions. in an arbitrary selection of 18 maternal sequences that are largely nonpolysomal in the ... | 1985 | 2415967 |
| dna methylation diminishes bleomycin-mediated strand scission. | three dna duplexes differing substantially in sequence were derived from pbr322 plasmid dna and supercoiled sv40 dna by digestion with appropriate restriction endonucleases. following treatment with the restriction methylase hhai (recognition sequence: gcgc) or hhai and hpaii (ccgg), the unmethylated and methylated dnas were compared as substrates for the antitumor agent bleomycin. bleomycin-mediated strand scission was shown to diminish substantially at a number of sites in proximity to the met ... | 1985 | 2416341 |
| characterization of mrna responsible for induction of functional sodium channels in xenopus oocytes. | when xenopus laevis oocytes were microinjected with poly(a)+ mrna isolated from adult rat brains or electric organs of electrophorus electricus, the oocytes developed functional sodium channels. upon application of veratrine, the microinjected oocytes exhibited transient depolarization, resulting in spontaneous repetitive spikes in some occasions, and action potentials. these responses were mediated mainly by external na ions, prolonged by scorpion toxin, completely blocked by tetrodotoxin, and ... | 1985 | 2416399 |
| rapid axonal transport in xenopus nerve in divalent cation free media. | an investigation was made of the effects of bathing media low in divalent cations on rapid axonal transport in the sciatic nerve of the amphibian xenopus laevis. the anterograde transport of a pulse of [35s]methionine proteins was observed using a multiple proportional counter as the detector. organelles undergoing anterograde and retrograde transport were detected by light microscopy. the structure of nerve fibers was examined by light and electron microscopy. there was no significant differenc ... | 1985 | 2416417 |
| developmental changes in keratin patterns during epidermal maturation. | the biochemical maturation of the epidermis of xenopus laevis was examined through an identification of the keratins expressed at selected stages of development. the keratin patterns obtained were compared to those observed in the adult epidermis and two xenopus non-epidermal, epithelial cell lines. the keratins expressed during development can be grouped into three classes: (1) keratins which are restricted to the embryonic epidermis (58 and 59 kda); (2) keratins which are prominent during deve ... | 1985 | 2416614 |
| changes in rna titers and polyadenylation during oogenesis and oocyte maturation in xenopus laevis. | the titers of over 90 sequences isolated by cdna cloning of oocyte poly(a)+rna were examined during oogenesis in xenopus laevis. the relative titers of most sequences in unfertilized eggs are established in pre-lamp brush oocytes and persist throughout oogenesis. we have identified several sequences whose titers decrease significantly during the growth phase of oogenesis as well as a few sequences whose titers increase slightly during this period. among 21 sequences analyzed by rna gel blots, al ... | 1985 | 2416617 |
| translation and functional expression of cell-cell channel mrna in xenopus oocytes. | mrna from estrogen-stimulated rat myometrium, a tissue known to upregulate cell-cell channels in response to this hormone, was microinjected into xenopus laevis oocytes. the oocytes had been freed from covering layers of follicle cells and vitelline to allow direct cell membrane interactions when paired. about 4 hours after the mrna injection, paired oocytes become electrically coupled. this coupling was due to the presence of typical cell-cell channels characterized by size-limited intercellula ... | 1985 | 2416937 |
| [primary structure of the alpha subunit of na+,k+-atpase. ii. isolation, reverse transcription and cloning of messenger rna]. | messenger rna, coding for the alpha-subunit of the na+, k+-atpase, was isolated from outer medulla of pig kidney. within 25s-26s region the mrna yields a band of specific hybridization with three oligonucleotide probes synthesized according to data on structures of three peptides isolated from the tryptic hydrolysate of the protein. translation of the enriched poly(a+)-fraction of rna in xenopus laevis oocytes followed by the immunochemical identification of the products confirmed the presence o ... | 1985 | 2417606 |
| developmentally regulated cytokeratin gene in xenopus laevis. | we have determined the sequence of cloned cdnas derived from a 1,665-nucleotide mrna which transiently accumulates during xenopus laevis embryogenesis. computer analysis of the deduced amino acid sequence revealed that this mrna encodes a 47-kilodalton type i intermediate filament subunit, i.e., a cytokeratin. as is common to all intermediate filament subunits so far examined, the predicted polypeptide, named xk70, contains n- and c-terminal domains flanking a central alpha-helical rod domain. t ... | 1985 | 2426572 |
| toxin gamma of the scorpion tityus serrulatus modifies both activation and inactivation of sodium permeability of nerve membrane. | the effects of the major neurotoxic fraction isolated from scorpion venom of tityus serrulatus, titx gamma, on peripheral nerve membrane of xenopus laevis were studied under current- and voltage-clamp conditions. 700 nmol/l titx gamma depolarized the membrane and induced spontaneous activity (150 s-1, maximum value), which ceased within a few minutes. it reduced the amplitude of the action potentials from 109 mv to 52 mv and increased their duration from 1.25 ms to 4.5 ms. 440 nmol/l titx gamma ... | 1986 | 2426654 |
| some properties of the contractile system and sarcoplasmic reticulum of skinned slow fibres from xenopus muscle. | properties of both the contractile system and the sarcoplasmic reticulum (s.r.) of slow fibres from the iliofibularis muscle of xenopus laevis were examined by using 'skinned' preparations mainly at 4 degrees c and ph 7.0. the results were compared with those of skinned fast fibres. the contractile system was activated with various concentrations of alkaline earth metal ions and it was found that the sensitivity of the contractile system of slow fibres to sr2+ and ba2+ was much higher than that ... | 1986 | 2427691 |
| cyclic adenosine monophosphate, calcium, acetylcholine and the current induced by adenosine in the xenopus oocyte. | the k+ current response to bath-applied adenosine has been studied on follicle-enclosed full grown oocytes from xenopus laevis, using the two electrodes voltage-clamp technique. the response to adenosine was mimicked by forskolin, an activator of adenylate cyclase. forskolin applied at low concentration potentiated the response to adenosine. at low concentration, isoprenaline, a beta-adrenergic agonist known to induce a potassium current via a rise of adenosine 3',5'-phosphate (cyclic amp) into ... | 1986 | 2427707 |
| cloning of cdna and amino acid sequence of a cytokeratin expressed in oocytes of xenopus laevis. | using a cdna clone from the ovary of the frog, xenopus laevis, we have identified the mrna and determined the complete amino acid sequence of a major cytoskeletal protein expressed in the oocyte. a comparison with other cytoskeletal proteins of xenopus and mammals identifies this polypeptide mr 55,700 as a nonepidermal kind of cytokeratin of the basic (type ii) subfamily, which represents the amphibian equivalent to cytokeratin no. 8 of simple epithelia of higher mammals. the sequence data demon ... | 1986 | 2428034 |
| mapping of neural crest pathways in xenopus laevis. | 1986 | 2428061 | |
| in vitro translation of b-cell stimulatory factor-1 in xenopus laevis oocytes. | b-cell stimulatory factor-1 (bsf-1) can be translated in vitro in xenopus laevis oocytes. this activity is blocked by an antibody to bsf-1. the rna species coding for bsf-1 activity sediments of approximately 8-9s and is separable from rna coding for interleukin-2 activity which sediments at approximately 11.5s. finally, the fact that bsf-1 can be translated in vitro confirms that functions attributed to bsf-1 do not depend on contamination with other biologically active molecules such as phorbo ... | 1986 | 2428526 |
| changes in intracellular calcium and in membrane currents evoked by injection of inositol trisphosphate into xenopus oocytes. | intracellular calcium was monitored by the use of aequorin in voltage-clamped oocytes of xenopus laevis. injection of inositol trisphosphate (ip3) into oocytes elicited slowly rising and decaying aequorin/calcium signals and produced oscillatory chloride membrane currents. these responses did not depend upon extracellular calcium, since they could be elicited in calcium-free solution and after addition of cobalt or lanthanum to block calcium channels in the surface membrane. we conclude that ip3 ... | 1986 | 2429327 |
| a ganglioside species (gd1 alpha) migrates at a slow rate and cmp-sialic acid severalfold faster in xenopus sciatic nerve: fluorographic demonstration. | the ninth dorsal root ganglion of adult xenopus laevis was labeled with n-acetyl-d-[6-3h]mannosamine, and intraaxonal migration of gangliosides was examined by analysis of the chloroform/methanol extract of each of 5-mm consecutive nerve segments by tlc coupled with fluorography. a unique disialoganglioside (gd1 alpha), which amounted to up to 83% of the total ganglioside in this nerve, migrated at 1-2 mm/day at 15 degrees c. this contrasts with the rapid transport of other ganglioside species p ... | 1986 | 2430059 |
| stage-specific keratins in xenopus laevis embryos and tadpoles: the xk81 gene family. | this report describes the isolation and characterization of genomic and cdna clones which define a subfamily of type i keratins in xenopus laevis whose expression is restricted to embryonic and larval stages. the xk81 subfamily, named after the prototype cdna clone dg81, contains four members arranged in two pairs of closely homologous loci; they were named 81a1, a2, b1, and b2. genomic clones were obtained representing all of these regions. the a1 gene has been completely sequenced together wit ... | 1986 | 2430981 |
| differential order of replication of xenopus laevis 5s rna genes. | in xenopus laevis there are two multigene families of 5s rna genes: the oocyte-type 5s rna genes which are expressed only in oocytes and the somatic-type 5s rna genes which are expressed throughout development. the xenopus 5s rna replication-expression model of gottesfeld and bloomer (cell 28:781-791, 1982) and wormington et al. (cold spring harbor symp. quant. biol. 47:879-884, 1983) predicts that the somatic-type 5s rna genes replicate earlier in the cell cycle than do the oocyte-type genes. h ... | 1986 | 2431292 |
| the appearance and distribution of intermediate filament proteins during differentiation of the central nervous system, skin and notochord of xenopus laevis. | antibodies against various intermediate filament proteins have been used to follow cell differentiation in the early xenopus embryo. three new monoclonal antibodies against xenopus cytokeratins raised against triton-insoluble material from tadpoles (rd35/2a, rd35/3a and d3/3a), two antibodies against mammalian cytokeratins (le65 and lp3k), monoclonal anti-(rat 200 k neurofilament protein), rabbit anti-(rat glial filament acidic protein), and rabbit antibodies to hamster and calf vimentin were us ... | 1986 | 2432146 |
| pigment cell pattern formation in amphibian embryos: a reexamination of the dopa technique. | neural crest-derived melanophores form species-specific patterns in the dermis of amphibian embryos. melanophore patterns may be generated by one of two general mechanisms: pigment cell precursors disperse throughout the embryo, with melanophores differentiating in certain regions due to environmental cues, or melanoblasts may localize in different regions as a result of a hierarchy of tissue affinities. both of these mechanisms have been proposed to be responsible for the dorso-ventral patterni ... | 1986 | 2432154 |
| patch clamp measurements on xenopus laevis oocytes: currents through endogenous channels and implanted acetylcholine receptor and sodium channels. | functional acetylcholine receptor (achr) and sodium channels were expressed in the membrane of xenopus laevis oocytes following injection with poly(a)+-mrna extracted from denervated rat leg muscle. whole-cell currents, activated by acetylcholine or by depolarizing voltage steps had properties comparable to those observed in rat muscle. oocytes injected with specific mrna, transcribed from cdna templates and coding for the achr of torpedo electric organ, expressed functional achr channels at a m ... | 1986 | 2432468 |
| cytokeratin expression in simple epithelia. iii. detection of mrnas encoding human cytokeratins nos. 8 and 18 in normal and tumor cells by hybridization with cdna sequences in vitro and in situ. | we describe cdna clones of mrnas encoding human cytokeratins nos. 8 and 18, and the amino acid sequences deduced from their nucleotide sequences. human cytokeratin no. 8 is a typical cytokeratin of the basic (type ii) subfamily, which is highly homologous to the corresponding bovine and amphibian (xenopus laevis) proteins; however, unlike the amphibian protein, it does not contain glycine-rich oligopeptide repeats in its carboxyterminal 'tail' domain. comparison with the reported amino acid sequ ... | 1986 | 2434381 |
| calmodulin synthesis and accumulation during oogenesis and maturation of xenopus laevis oocytes. | the calmodulin levels in stage 6 xenopus oocytes averaged 89 +/- 24 (sd) ng/oocyte and had largely accumulated by stage 3 of oogenesis. from stage 3 to early stage 6, calmodulin levels did not increase further. however, in large stage 6 oocytes (greater than 1.25 mm diam) calmodulin levels again rose to a level as high as 121 ng/oocyte. calmodulin levels did not change during the maturation of stage 6 oocytes and the results of measurements on animal and vegetal oocyte halves from control and ma ... | 1986 | 2417900 |
| evidence for a d2 dopamine receptor in frog retina that decreases cyclic amp accumulation and serotonin n-acetyltransferase activity. | the regulation of serotonin n-acetyltransferase (nat) activity and cyclic amp accumulation in the retina of the african clawed frog (xenopus laevis) was studied using an in vitro eye cup preparation. retinal nat, a key enzyme in the synthesis of melatonin, is expressed as a circadian rhythm with peak activity at night. the increase of nat activity at night appears to be mediated by cyclic amp and is suppressed by light. dopamine inhibits the nocturnal increase of retinal nat activity; approximat ... | 1986 | 2418326 |
| characterization of rna-protein interactions in 7 s ribonucleoprotein particles from xenopus laevis oocytes. | 5 s rna interactions with transcription factor protein a (tfiiia) in 7 s particles from xenopus laevis oocytes (xlo) have been characterized by the use of an in vitro rna exchange assay. 32p-labeled xlo 5 s rna can rapidly be incorporated into 7 s particles by simple incubation of the rna with intact particles. incorporation of the labeled rna during exchange reaches an equilibrium within 20 min at 20 degrees c. labeled xlo 5 s rna already incorporated in 7 s particles can be chased out by an ex ... | 1986 | 2419324 |
| a dispersed tyrosine trna gene from xenopus laevis with high transcriptional activity in vitro. | several kinds of trna genes of xenopus laevis are clustered together within tandemly repeated 3.18-kilobase dna fragments. other members of these reiterated trna gene families are dispersed and irregularly arranged in the genome. here we report the isolation and some characteristics of one such dispersed gene that codes for a tyrosine trna. it is located within a low copy number 9.4-kilobase restriction fragment that contains no other rna polymerase iii gene functional in vitro. the dispersed ge ... | 1986 | 2416752 |
| cyclic amp stimulates serotonin n-acetyltransferase activity in xenopus retina in vitro. | the possible involvement of cyclic amp in the regulation of retinal serotonin n-acetyltransferase (nat) activity was investigated using eye cups of xenopus laevis cultured in a defined medium. addition of dibutyrylcyclic amp (dbcamp) increased retinal nat activity in eye cups cultured in light. addition of adenosine or 5'-amp under identical conditions was without effect. 3-isobutylmethylxanthine (ibmx) increased both retinal cyclic amp levels and nat activity in light-exposed eye cups. forskoli ... | 1986 | 2415681 |
| involvement of calcium in the regulation of serotonin n-acetyltransferase in retina. | the possible involvement of calcium in the regulation of retinal serotonin n-acetyltransferase (nat) activity was investigated using eye cups of xenopus laevis cultured in defined medium. omitting cacl2 from the culture medium completely inhibited the dark-dependent increase of nat activity at night. approximately 10(-4)-10(-3) m free ca2+ was found to be required for the maximal increase of nat activity in the dark. other divalent cations--ba2+, sr2+, and mn2+--did not substitute for ca2+. anta ... | 1986 | 2415684 |
| the nuclear lamins. a multigene family of proteins in evolution and differentiation. | the nuclear lamina consists of a proteinaceous layer or meshwork situated subjacent to the inner nuclear membrane. it is a karyoskeletal structure formed by a polymer containing one to three major polypeptides collectively termed the lamins. in all cells examined of vertebrates and invertebrates, the lamins exhibit very similar mr ranging from 60 000 to 80 000. in vertebrates, two groups of lamins can be distinguished by their isoelectric value, one being near-neutral and the other acidic (isoel ... | 1986 | 2415378 |
| mauthner neurons survive metamorphosis in anurans: a comparative hrp study on the cytoarchitecture of mauthner neurons in amphibians. | giant medullary neurons were revealed in adult xenopus laevis and rana esculenta following hrp injections to the spinal cord. these neurons were identified as mauthner neurons because (1) they have the same position and orientation as the larval mauthner neurons, i.e., they lie at the level of the viiith nerve root. (2) they have two large dendritic trees that for each species are similar to those of the larval mauthner neurons, (3) they are clearly distinguishable from other large reticular neu ... | 1986 | 3081602 |
| valproate reduces excitability by blockage of sodium and potassium conductance. | effects of the antiepileptic drug valproate on sodium and potassium currents in the nodal membrane of peripheral nerve fibers of xenopus laevis were determined by voltage- and current-clamp experiments. under voltage-clamp conditions, a reduction of both sodium and potassium conductance (in a ratio of 2:1) was observed. typically, 2.4 mm (400 mg/l) valproate reduced the sodium current 54% and the potassium current 26%, at a membrane potential of 5 mv. valproate did not affect the leakage conduct ... | 1986 | 3084227 |
| a mass spectrometric method for the identification of novel peptides in xenopus laevis skin secretions. | the peptides secreted by the south african frog xenopus laevis were screened systematically using a strategy based on fabms. hplc of crude and sephadex g-10 chromatographed secretions showed that many more peptides were present in these secretions than those previously identified, i.e., xenopsin, caerulein, trh, and pgla. fractions from the hplc were analyzed directly by fabms to determine the molecular weights of these novel peptides. subsequent analyses, using a combination of fabms, manual ed ... | 1986 | 3084710 |
| the cellular distribution of histone h5 in embryonic and adult tissues of xenopus laevis and chicken. | the cellular distribution of histone h5 in embryonic and adult tissues of xenopus laevis and chicken has been established with monoclonal antibodies to histone h5. both in xenopus and in chicken, the protein has presumably a more widespread cellular distribution than hitherto expected but is absent in most embryonic tissues. at least in xenopus its presence seems not to be restricted to amitotic cells. arguments will be put forward histone h5 in these animals should be considered as a h1(0) type ... | 1986 | 3085145 |
| spatial domains within the early xenopus laevis embryo revealed by in situ hybridization and monoclonal antibodies. | 1986 | 3085157 | |
| cell surface carbohydrate involvement in controlling the adhesion and morphology of neural crest cells and melanophores of xenopus laevis. | pieces of dorsal neural tube (stages 22-23) or late neural crest tissue (stages 24-26) of xenopus laevis were cultured. migratory cells moved out of explants to form an outgrowth of multipolar melanophores on the substratum. treatment with beta-galactosidase (0.1-0.4 u/ml) to remove cell surface galactose was correlated with detachment of melanophores. in the presence of lower concentrations of this enzyme the shapes of these cells were converted to arborized, spidery morphologies and cell movem ... | 1986 | 3086486 |
| aerobic and anaerobic correlates of mechanical work by gastrocnemius muscles of the aquatic amphibian xenopus laevis. | isolated, saline-perfused gastrocnemius muscles of xenopus laevis were used to assess the relationships between aerobic and anaerobic metabolism during conditions of rest, isotonic contraction and recovery. the major part (85%) of the energy used during 25 min of isotonic contractions in the saline-perfused muscles was from anaerobic rather than aerobic sources. however, the small contribution made by oxidative metabolism during activity can be attributed, in part at least, to limitations impose ... | 1986 | 3088193 |
| processing of the thyrotropin releasing hormone (trh) precursor in xenopus skin and bovine hypothalamus: evidence for the existence of extended forms of trh. | acid extracts of xenopus laevis skin were fractionated by gel filtration on sephadex g50 ion-exchange chromatography and reverse-phase high performance liquid chromatography (hplc). peptides related to thyrotropin releasing hormone (trh) were identified in the eluted fractions by trypsin digestion and radioimmunoassay (ria) using antibodies to the trh tripeptide pglu-his-pro amide or to a trh-related pentapeptide pglu-his-pro-gly-lys. in addition to the tripeptide hormone, evidence was obtained ... | 1986 | 3088682 |
| the vitelline envelope to fertilization envelope conversion in eggs of xenopus laevis. | fertilization of the xenopus laevis egg causes the conversion of the vitelline envelope to the fertilization envelope, a change reflected in the loss of sperm penetrability of the egg and the appearance of an electron-dense layer on the outer aspect of the fertilization envelope. as seen by one-dimensional gel electrophoresis, two components with molecular weights of 69,000 and 64,000 in the vitelline envelope were converted to 66,000 and 61,000 in the fertilization envelope. by two-dimensional ... | 1986 | 3089852 |
| determination of human factor viii (ahg-associated protein)--antigen in endothelial cells from xenopus laevis (xth cells). evaluation of a sensitive elisa technique. | ahg-associated protein (ahg-a.p.), the antigen of the blood-clotting factor viii complex, is a specific endothelial cell marker. primary (p-xth) and established (xth-2) endothelial cells from the hearts of xenopus laevis tadpoles were assayed for the presence of this marker by means of immunological cross-reaction (recognition of common antigenic sites) with antiserum against human ahg-a.p. radial immunodiffusion and rocket immunoelectrophoresis proved to be insufficiently sensitive, whereas imm ... | 1986 | 3091251 |
| the synthesis and expression of hla-a and -b antigens in xenopus laevis oocytes. | purified mrna's encoding the hla-a and -b antigen heavy chains or beta 2-microglobulin were prepared from human b lymphoid cells by positive hybridization selection procedures. the role of chain association in the biosynthesis and intracellular transport of hla-a and -b antigens was investigated by injecting these mrna species into xenopus laevis oocytes and following the fates of the translated products by immunoprecipitation. when mrna encoding beta 2-microglobulin from the b lymphoblastoid ce ... | 1986 | 3092030 |
| subunit structure of a cortical granule lectin involved in the block to polyspermy in xenopus laevis eggs. | the cortical granule lectin of xenopus laevis eggs is a large molecular mass glycoprotein involved in the post-fertilization block to polyspermy. we have investigated the subunit structure of this lectin and found that the native molecule contains 10-12 monomers, each of which has considerable charge and size heterogeneity due to glycosylated side chains. in addition, significant amino acid sequence homology is indicated by peptide mapping of subunits separated by isoelectric focusing. | 1986 | 3093279 |
| isolation and characterization of a lectin from the cortical granules of xenopus laevis eggs. | a cortical granule lectin was isolated from eggs of the south african clawed toad xenopus laevis. the lectin was released from the cortical granules by activation of dejellied eggs with the ca2+ ionophore a23187. the lectin was purified by affinity chromatography with its natural ligand, the egg jelly coat, chemically coupled to a sepharose matrix. the purified lectin was homogeneous by the criteria of isoelectric focusing (pi = 4.6), immunodiffusion, and immunoelectrophoresis but existed in two ... | 1986 | 3098282 |
| periodic changes in the rigidity of activated anuran eggs depend on germinal vesicle materials. | the eggs of xenopus laevis and bufo bufo japonicus matured in vitro by progesterone were denuded and activated by electrical shock or pricking, and their diameters were determined periodically until the postactivation time equivalent to the 8- to 16-cell stage. normally matured eggs showed a quick rounding-up and flattening immediately after activation (activation response), followed by a periodic flattening and rounding-up (postactivation response) corresponding to the intervals of early cleava ... | 1986 | 3098597 |
| gas exchange, storage and transport in voluntarily diving xenopus laevis. | a closed, extracorporeal loop, containing oxygen and carbon dioxide electrodes, was developed in order to make continuous measurements of lung gas po2 (pao2) and pco2 (paco2) in undisturbed xenopus laevis. pulmonary r values (delta paco2/delta pao2) are about 0.8 during periods of lung ventilation in resting animals, but they fall very rapidly as a voluntary dive proceeds. in fact, the instantaneous r values for lung eventually fall to zero during a voluntary dive, since pao2 continues to declin ... | 1986 | 3100713 |
| globin evolution in the genus xenopus: comparative analysis of cdnas coding for adult globin polypeptides of xenopus borealis and xenopus tropicalis. | globin mrnas of xenopus borealis and xenopus tropicalis have been cloned and sequenced. the nucleotide and derived amino acid sequences were compared with each other and with already available data from xenopus laevis. this analysis rendered clear evidence that the common ancestor of x. laevis and x. borealis, but not of x. tropicalis, had lost one amino acid of the beta-globins prior to a genome duplication event that preceded the segregation of the former two species. replacement-site substitu ... | 1986 | 3100812 |
| the ribosomal spacer in xenopus laevis is transcribed as part of the primary ribosomal rna. | s1 mapping of xenopus laevis ribosomal rna transcripts, both in oocyte microinjection experiments and in vivo, shows that all but 212 bp of the so-called "non-transcribed" spacer (nts) of the ribosomal dna repeat is transcribed as part of the primary ribosomal transcript. the 40s pre-ribosomal rna (pre-rrna) is therefore a processing intermediate. the primary ribosomal transcript co-terminates with the previously described spacer transcripts [moss], at a site 213 bp upstream of the 40s pre-rrna ... | 1986 | 3018668 |
| sequence analysis of the larval beta ii-globin gene of xenopus laevis. | the 1822 bp sequence of the larval xenopus laevis beta ii-globin gene is reported together with 240 bp upstream of the gene and 190 bp beyond the site of polyadenylation. the mrna start point was determined by primer extension as well as nuclease s1 mapping and the polyadenylation site by comparison of the gene sequence to the mrna sequence derived from a corresponding cdna clone. like other vertebrate globin genes, this gene comprises three exons interrupted by two intervening sequences (ivs). ... | 1986 | 3020391 |
| induction of taurine responsiveness in xenopus oocytes by messenger rna from mouse brain. | a taurine response was induced in the surface membrane of the oocytes of xenopus laevis by injection of the mrna from the neonatal mouse brain, and the response was studied electrophysiologically. the permeability of mrna-injected oocytes to chloride ions was increased by the application of taurine in a dose-dependent manner. the same oocyte also responded to gaba, but bicuculline suppressed only the gaba response. these results suggest a possibility that taurine could be a neurotransmitter of c ... | 1986 | 3020479 |
| dna replication in vitro erases a xenopus 5s rna gene transcription complex. | replication of the xenopus laevis 5s rna gene in vitro is unimpeded by the presence of a complete transcription complex assembled on the internal control region of the gene. the transcription complex is disrupted by passage of the replication fork, specific transcription factors are displaced, and the daughter 5s rna genes are inactivated. we have been unable to demonstrate that any "memory" of the preexisting transcription complex is transmitted to the daughter dna duplexes following replicatio ... | 1986 | 3021334 |
| tx1: a transposable element from xenopus laevis with some unusual properties. | a family of transposable genetic elements in the genome of the frog, xenopus laevis, is described. they are designated tx1. transposability of the elements was deduced by characterization of a chromosomal locus which is polymorphic for the presence or absence of a tx1 element. nucleotide sequence analysis suggested that tx1 elements show target site specificity, as they are inserted at the pentanucleotide tttaa in all four cases that were examined. the elements appear to have 19-base-pair (bp) i ... | 1986 | 3022140 |
| structural analysis of ribosomal dna homologues in nucleolus-less mutant of xenopus laevis. | sequences homologous to the ribosomal dna (rdna) in a xenopus anucleolate (nucleolus-less) mutant were analyzed by southern blot analysis. the mutant was found to possess a variety of sequences homologous to non-transcribed spacer (nts) and/or coding region of rdna. 65 rdna-homologous clones were isolated from a genomic dna library of the mutant. all the clones showed only partial homology to the normal rdna unit and their restriction maps differed from that of the normal rdna unit. based on the ... | 1986 | 3023192 |
| accurate in vitro transcription of xenopus laevis mitochondrial dna from two bidirectional promoters. | the mitochondrial rna polymerase from xenopus laevis oocytes was partially purified by heparin-sepharose chromatography and phosphocellulose chromatography. this rna polymerase preparation specifically initiated the transcription of x. laevis mitochondrial dna (mtdna) from two bidirectional promoters contained within a 123-base-pair segment of the mtdna between the heavy-strand replication origin and the rrna cistrons. transcription in vitro initiated from precisely the same start sites previous ... | 1986 | 3023938 |
| conserved sequence motifs upstream from the co-ordinately expressed vitellogenin and apovldlii genes of chicken. | the vitellogenin and apovldlii yolk protein genes of chicken are transcribed in the liver upon estrogenization. to get information on putative regulatory elements, we compared more than 2 kb of their 5' flanking dna sequences. common sequence motifs were found in regions exhibiting estrogen-induced changes in chromatin structure. stretches of alternating pyrimidines and purines of about 30-nucleotides long are present at roughly similar positions. a distinct box of sequence homology in the chick ... | 1986 | 3024115 |
| formation of the 3' end on u snrnas requires at least three sequence elements. | the structural requirements for 3' end formation on the xenopus laevis u1b snrna gene have been studied. three sequence elements are shown to be required. the first is a conserved sequence element found immediately 3' of all vertebrate u snrna genes studied so far. the second is a gene internal sequence potentially capable of forming a stem-loop structure close to the 3' end of the rna. the third element lies upstream of these, and may be part of the gene promoter. experiments designed to invest ... | 1986 | 3024969 |
| the pituitary adrenocorticotropes originate from neural ridge tissue in xenopus laevis. | a series of grafting experiments was conducted to determine pituitary origins prior to brain tube closure in xenopus laevis. extirpation experiments indicated that the ventral neural ridge (vnr) tissue of stage-18+ embryos was essential for pituitary development. bolton-hunter reagent was used to label stage-18+ vnr tissue with 125i, and this tissue was then returned to the donor and its subsequent ontogenesis followed. labelled tissue was ultimately found in the ventral hypothalamus, the ventra ... | 1986 | 3025328 |
| structural and functional analysis of chicken u4 small nuclear rna genes. | two distinct chicken u4 rna genes have been cloned and characterized. they are closely linked within 465 base pairs of each other and have the same transcriptional orientation. the downstream u4 homology is a true gene, based on the criteria that it is colinear with chicken u4b rna and is expressed when injected into xenopus laevis oocytes. the upstream u4 homology, however, contains seven base substitutions relative to u4b rna. this sequence may be a nonexpressed pseudogene, but the pattern of ... | 1986 | 3025618 |
| sequences involved in accurate and efficient transcription of human c-myc genes microinjected into frog oocytes. | by microinjecting a series of deletion mutant constructs into xenopus laevis oocytes, transcriptional control regions, two promoters, of the human c-myc gene were defined. in the case of the first promoter, sequences between -60 and -37 relative to the transcription start site contained an element essential for promoter activity. in the case of the second promoter, sequences between -66 and -56 relative to the initiation site appeared to be involved in accurate and efficient transcription. in bo ... | 1986 | 3025632 |
| [transcription, in frog oocytes and transgenic mice, of recombinant plasmids with long terminal repeats of retrovirus proviruses]. | rna-dna hybridization was used to study the transcription efficiency of the genes controlled by the long terminal repeats (ltr) from two different retroviral proviruses (exogenous provirus of the chicken rous sarcoma virus and endogenous xenotropic provirus of the mouse). the oocyte nuclei of xenopus laevis and the liver of transgenic mice were used as the transcription systems. the transcription efficiency of genes with the above mentioned promoters was shown to be roughly the same for both sys ... | 1986 | 3025678 |
| dexamethasone and estrogen regulate xenopus laevis albumin mrna levels. | the regulation of albumin mrna levels by steroid hormones was examined in a primary xenopus liver culture system. in the absence of exogenous steroid hormone, albumin mrna levels declined rapidly in culture. dexamethasone is required for preservation of albumin mrna levels in culture and effects a greater than 10 fold induction of albumin mrna in cultures maintained in steroid hormone-free medium. estrogen can override the effect of dexamethasone and elicits a decline of greater than 80% in albu ... | 1986 | 3010979 |
| cyclic amp and cell differentiation in amphibian embryonic explants. | conflicting results have been published concerning the effects of cyclic nucleotides on amphibian cell differentiation. here we report the effects of cyclic adenosine monophosphate (camp) and dibutyryl-cyclic adenosine monophosphate (db-camp) on isolated explants from late blastulae of ambystoma mexicanum and xenopus laevis. both camp and db-camp (10(-4)-10(-9) m) promote 'neuralizing' differentiation in ambystoma explants. xenopus explants treated with the nucleotides (10(-4), 10(-6), 10(-8) m) ... | 1986 | 3011532 |
| cnpase activity in the vertebrate retina, retinal pigmented epithelium, and choroid. | the activity of the enzyme 2',3'-cyclic nucleotide 3'-phosphohydrolase (cnpase, e.c.3.1.4.37) has been studied in the retina of three vertebrate species. activity was highest in the goldfish, followed by xenopus laevis and rana pipiens. also, high activity levels were found in goldfish retinal pigment epithelium and choroid, but not in the other two species. when added to in vitro culture systems, 2',3'-cyclic nucleotides were found to have no effect on goldfish cone retinomotor movement, but ca ... | 1986 | 3011952 |
| some primary olfactory axons project to the contralateral olfactory bulb in xenopus laevis. | cobaltous lysine and horseradish peroxidase (hrp) were used to trace primary olfactory axons to their terminations. the tracers were taken up in the olfactory mucosa and transported to the olfactory bulb. the results suggest that either hrp or cobaltous-lysine methods are useful and simple tools for studying such connections. in addition to the ipsilateral projection, we report here for the first time a projection to the medial part of the contralateral olfactory bulb. the overlaps of ipsi- and ... | 1986 | 3012418 |
| recbc, sbcb independent, (at)n-mediated deletion of sequences flanking a xenopus laevis beta globin gene on propagation in e. coli. | plasmids containing sequences 3' of the adult beta 1 globin gene of xenopus laevis are unstable on propagation in a range of e. coli host strains. up to 300 bp of xenopus dna are lost by rec a independent recombination between (at)37 and (at)17 sequences. additionally, smaller deletions occurring in or around the (at)37 sequence are observed. deletion of these potential cruciform structures occurs in the absence of exonuclease i, exonuclease v and exonuclease viii as the same pattern of deletion ... | 1986 | 3012463 |
| identification of initiation sites for transcription of xenopus laevis mitochondrial dna. | the sites of transcription initiation for xenopus laevis mtdna have been mapped using in vitro capping and primer extension analysis of rna isolated from oocytes. transcription of the heavy strand initiates predominantly at a site 33 nucleotides upstream of the trnaphe gene. this promoter is bidirectional, with transcription of the light strand initiating only one base pair away. a second, more predominant light strand promoter is located 70 nucleotides away from the major heavy strand promoter. ... | 1986 | 3013854 |
| conserved sequences and cell-specific dnase i hypersensitive sites upstream from the co-ordinately expressed alpha i- and alpha ii-globin genes of xenopus laevis. | the globin gene family of xenopus laevis comprises pairs of closely related genes that are arranged in two clusters, each pair of genes being co-ordinately and stage-specifically expressed. to get information on putative regulatory elements, we compared the dna sequences and the chromatin conformation 5' to the co-ordinately expressed adult alpha-globin genes. sequence analysis revealed a relatively conserved region from the cap site up to position -289, and further upstream seven distinct boxes ... | 1986 | 3014154 |
| neurohypophysial peptide potencies in cultured anuran epithelia (a6). | to characterize the v2 receptor (for antidiuretic hormone), we have studied the effect of a number of neurohypophysial hormone analogues on cyclic amp (camp) accumulation and short-circuit current in cultured epithelia formed by a6 cells. a6 is the designation of a continuous cell line derived from the kidney of xenopus laevis. the order of potency for stimulating camp accumulation and short-circuit current in a6 epithelia is like that for stimulating water permeability in toad urinary bladder. ... | 1986 | 3014910 |
| synaptic organization of dorsal root projections to lumbar motoneurons in the clawed toad (xenopus laevis). | synaptic connexions between dorsal root primary afferents and lumbar motoneurons have been investigated in the isolated spinal cord of the clawed toad. the study of monosynaptic actions evoked in motoneurons by 9th or 10th dorsal root stimulation or by impulses in single primary afferents provided evidence for both electrical and chemical junctional transmission at the sensory-motor synapses. the anterograde filling of the 9th and 10th dorsal roots with horseradish peroxidase (hrp) shows that af ... | 1986 | 3015652 |
| major transitions in histone gene expression do not occur during development in xenopus laevis. | in light of the parallels that exist in the structure of histone genes in sea urchins and in the frog, xenopus laevis, and in the early development of these animals, it has been thought that xenopus histone gene expression might be subject to the type of developmental regulation observed in sea urchins. we have examined the patterns of histone mrna accumulation in xenopus oocytes and embryos by primer extension and s1 nuclease protection techniques. the data demonstrate that histone genes which ... | 1986 | 3015703 |
| cloning and sequencing of mrnas coding for two adult alpha globin chains of the salamander pleurodeles waltlii. | a cdna library of erythrocyte mrnas was established from immature red blood cells of the adult amphibian, pleurodeles waltlii (urodele; salamander). the cdna clones corresponding to the four adult globin chains were first identified and characterized by positive selection and the cdnas derived from the two (major and minor) alpha-globin chains sequenced. the sequences presented contain both the complete 3'-noncoding region and the coding region of both chains, with the exception of the first nin ... | 1986 | 3015729 |
| voltage dependence of the rheogenic na+/k+ atpase in the membrane of oocytes of xenopus laevis. | electrophysiological experiments were performed to analyze the na+/k+-atpase in full-grown prophase-arrested oocytes of xenopus laevis. if the na+/k+-atpase is inhibited by dihydroouabain (dho), the resting potential of the membrane of na+-loaded oocytes may depolarize by nearly 50 mv. this hyperpolarizing contribution to the resting potential depends on the degree of activation of the na+/k+-atpase and varies with intracellular na+ activity (aina) and extracellular k+ (k+o). it is concluded tha ... | 1986 | 3016280 |
| comparative development of end-plate currents in two muscles of xenopus laevis. | the development of miniature end-plate currents (m.e.p.c.s) was studied in the superior oblique and interhyoideus muscles of xenopus laevis. an analysis of m.e.p.c. decays shows that each muscle possesses its own characteristic programme of end-plate current development. in the superior oblique, the exponential decay constants of m.e.p.c.s were initially about 3 ms; they declined within half a day to 1 ms and remained at that value for six weeks. they then gradually became longer, reaching a mea ... | 1986 | 3018234 |
| in vitro transcription by xenopus oocytes rna polymerase iii requires a dna topoisomerase ii activity. | extracts of xenopus laevis oocytes are able to assemble minichromosomes in vitro when they are supplemented with atp and mg2+. we have followed the time course of in vitro dna supercoiling and transcription of polyoma virus closed circular dna. the transcriptional activity increased with the assembly time of chromatin in the presence of both atp and mg2+, but only residual activity was detected in the absence of either of them. we also found that polyoma dna as well as 5s rna gene transcription ... | 1986 | 3007112 |
| circadian rhythm of interrenal activity in xenopus laevis. | young specimens of xenopus laevis were kept under constant environmental conditions (artifical light from 600 to 1800 hr, feeding between 800 and 900 hr) and the concentrations of aldosterone and corticosterone in the serum were measured every 3 hr. furthermore, the kidneys containing the interrenals were removed and their corticosteroid release under stimulation by the pars distalis and mammalian acth was determined. under these conditions, the corticosteroid levels in the serum were maximal fr ... | 1986 | 3007269 |
| expression of ribosomal insertion in drosophila: sensitivity to intercalating drugs. | ribosomal insertions in drosophila are transcribed at very low levels. the abundance of the most prominent 0.8 kb type 1 insertion transcript increased up to 60-fold when cultured cells were exposed to the dna intercalating drug chloroquine. after injection of insertion-containing rdna in circular form into xenopus laevis oocytes an apparently identical 0.8 kb insertion transcript was synthesized, and its accumulation was stimulated several fold by coinjection of chloroquine or ethidium bromide. ... | 1986 | 3005969 |
| nucleotide sequence of the chicken 5-aminolevulinate synthase gene. | 5-aminolevulinate synthase, the first and rate-controlling enzyme of heme biosynthesis, is regulated in the liver by the end-product heme. to study this negative control mechanism, we have isolated the chicken gene for ala-synthase and determined the nucleotide sequence. the structural gene is 6.9 kb long and contains 10 exons. the transcriptional start site for ala-synthase was determined by primer extension analysis. a fragment of 291 bp from the 5' flanking region including 34 bp of the first ... | 1986 | 3005973 |
| nerve-induced remodeling of muscle basal lamina during synaptogenesis. | to identify mechanisms that regulate the deposition of the junctional basal lamina during synaptogenesis, immunocytochemical experiments were carried out on cultured nerve and muscle cells derived from xenopus laevis embryos. in some experiments successive observations were made on individual muscle cells after pulse-labeling with a fluorescent monoclonal antibody specific for a basal lamina proteoglycan. in others, old and new proteoglycan molecules were differentially labeled with antibody con ... | 1986 | 3005339 |
| conserved restriction sites within the ribosomal rna genes of vertebrates. | we have mapped the cleavage sites of four restriction enzymes which recognize six-base sequences within the nuclear ribosomal (rrna) genes of twelve vertebrates, including several placental mammals (homo sapiens, man; bos taurus, cow; equus caballus, horse; sus scofra, pig; ovis aries, sheep; rattus rattus, rat), a marsupial (didelphis marsupialis, opossum), a bird (gallus domesticus, chicken), an amphibian (xenopus laevis), a reptile (alligator mississipiensis), a bony fish (cynoscion nebulosus ... | 1986 | 3004584 |
| gabaergic regulation of melanocyte-stimulating hormone secretion from the pars intermedia of xenopus laevis: immunocytochemical and physiological evidence. | alpha-msh secretion from the amphibian pars intermedia is under inhibitory hypothalamic control, and the catecholamine dopamine is thought to be the physiological msh release-inhibiting factor. in the present study we evaluated the possible role of the neurotransmitter gamma-aminobutyric acid (gaba) in the regulation of the pars intermedia of xenopus laevis. immunocytochemical staining with antibodies to glutamic acid decarboxylase showed the presence of a rich gabaergic network in the intermedi ... | 1986 | 3000738 |
| trans effect of the e1 region of adenoviruses on the expression of a prokaryotic gene in mammalian cells: resistance to 5' -ccgg- 3' methylation. | the plasmid construct psvo-cat has been used to test adenovirus promoter activities in the unmethylated or methylated state. we have now observed that the e2a late promoter of adenovirus type 2 (ad2) dna also activated the chloramphenicol acetyltransferase (cat) gene upon transfection of the pad2e2a-cat construct into mammalian cells, and it was inactivated by specific methylations of three 5' -ccgg- 3' sites. similar results had been reported previously after microinjecting promoter-methylated ... | 1986 | 2937060 |
| changes in activity of the regulatory glycolytic enzymes and of the pyruvate-dehydrogenase complex during the development of xenopus laevis. | in this study we investigated the variations of the maximal activities of the rate-controlling glycolytic enzymes (i.e., hexokinase, hk; phosphofructokinase, pfk; pyruvate kinase, pk) and of the pyruvate-dehydrogenase complex (pdhc) during the early embryogenesis of xenopus laevis (from cleavage through hatching). all the enzymatic assays, using different coupled reactions, were performed spectrophotometrically on cytosolic and mitochondrial fractions. the maximal hk activity increases markedly ... | 1986 | 2937670 |
| the relationship between chromosomal origins of replication and the nuclear matrix during the cell cycle. | a cytological investigation into the dynamic behaviour of the origins of replication with respect to the nuclear matrix has been carried out on xenopus laevis cultured cells. in order to preferentially label origins or 'non-origin' regions along dna fibres, 5-fluoro-2'-deoxyuridine (fudr)-treated cells were pulsed with [3h]deoxyadenosine in early or late s phase. samples were then allowed to proceed through the cell cycle for increasing times. the dna loops were induced in situ to completely unc ... | 1986 | 2940105 |
| impaired rejection of minor-histocompatibility-antigen-disparate skin grafts and acquisition of tolerance to thymus donor antigens in allothymus-implanted, thymectomized xenopus. | we examine whether j strain xenopus laevis and x laevis/gilli (lg) isogeneic hybrids, thymectomized (tx) at 7 days and implanted with larval or postmetamorphic thymus (either normal or irradiated) in late larval life, can be used to explore the role of the developing thymus in the education of minor histocompatibility (h) antigen-reactive t cells and in the acquisition of tolerance to mhc (major histocompatibility complex) antigens. tx lg xenopus implanted with isogeneic thymus display fully res ... | 1986 | 2940739 |
| studies on dna polymerases of xenopus laevis oocytes: subcellular distribution and physical association of dna polymerase alpha inside the nucleus. | the localization of dna polymerases in xenopus laevis oocytes and eggs was studied. oocytes have a high level of dna polymerase alpha activity detected exclusively in the nuclei, while mitochondria contain all the dna polymerase activity of the gamma type. no dna polymerase beta activity is present in the nuclear fraction. moreover, the beta activity is not present in unfertilized eggs. in oocytes, dna polymerase alpha is weakly bound to the nucleoplasm. the leakage of the enzyme from whole nucl ... | 1986 | 2941095 |
| the development of inducer and effector immune suppressor cell function in xenopus laevis, the south african clawed toad: the effect of metamorphosis. | thymic capacity to induce suppression of antibody production by immunized xenopus laevis toadlet spleen fragments was tested in co-cultures for different developmental stages (nieuwkoop, p.d. and j. faber: normal table of xenopus laevis (daudin) (north holland, amsterdam) 1967). while thymuses of stages 52-54 (premetamorphosis) induced suppression, those of stages 58-62 (metamorphosis) did not. this capacity returned in metamorphic climax (stages 63-65). tests of lectin-induced suppressor functi ... | 1986 | 2941153 |
| monospecific antibodies reveal details of u2 snrnp structure and interaction between u1 and u2 snrnps. | monospecific antibodies directed against several u small nuclear ribonucleoprotein (u snrnp) particle proteins were affinity purified from a patient's anti-(u1,u2)rnp serum. these were used to demonstrate that: (i) proteins equivalent to the mammalian u2 snrnp-specific a' and b" proteins are present in xenopus laevis oocytes; (ii) both proteins a' and b" have the same structural requirements for binding to u2 snrna; (iii) proteins b, b' and d have the same structural requirement for binding to u ... | 1986 | 2941274 |
| formation of nucleus-like structure in the cytoplasm of lambda-dna-injected fertilized eggs and its partition into blastomeres during early embryogenesis in xenopus laevis. | the fate of bacteriophage lambda-dna was examined after injection into the fertilized eggs of xenopus laevis. injection of a large amount of lambda-dna (ca. 24 ng) into a fertilized xenopus egg induced the formation around the injected dna of a giant nucleus-like structure which was surrounded by an apparently normal bilayered nuclear membrane with nuclear pore complexes. southern blot analysis revealed the persistence of injected lambda-dna until the blastula stage. the nucleus-like structure w ... | 1986 | 2942430 |
| gene expression in transgenic xenopus laevis. | 1986 | 2944126 | |
| cap trimethylation of u snrna is cytoplasmic and dependent on u snrnp protein binding. | trimethyl capping of u2 snrna has been studied using u2 genes with mutations located in either the 5' flanking or the coding region. a monomethyl (7-methylguanosine) cap is added to u2 cotranscriptionally, trimethylation being posttranscriptional. the immediate 5' flanking sequences have no influence on trimethylation; furthermore, trimethylation is not affected by changing the position and sequence of the cap site. the efficiency of trimethylation is reduced by deleting the sm binding site from ... | 1986 | 2944599 |
| recombinant dna produced human il-2, injected in vivo, will substitute for carrier priming of helper function in the south african clawed toad, xenopus laevis. | the studied included in this report tested the ability of a recombinant dna produced human lymphokine (ril-2) to serve as a substitute for the carrier priming required for the in vivo generation of anti-hapten responses, in young adults of xenopus laevis, the south african clawed toad. heterologous erythrocyte carriers were used. immune reactivity was monitored with hapten-specific antigen binding cells (abc) in spleen cell suspensions, 8 days after injection i.p. of trinitrophenylated sheep ery ... | 1986 | 2945778 |