| identification of a tfiiia binding site on the 5' flanking region of the tfiiia gene. | xenopus transcription factor iiia (tfiiia) regulates 5s ribosomal rna gene transcription in a positive manner by binding to the internal control region (icr) of the 5s rna gene. the present study reports the identification of a tfiiia binding site on the 5' flanking region of the xenopus laevis gene that codes for the synthesis of this transcription factor. this tfiiia binding site (deduced from tfiiia-dependent alterations in dnase i protection patterns) extends on the 5' flanking region from a ... | 1990 | 2349091 |
| raman spectroscopy of synthetic antimicrobial frog peptides magainin 2a and pgla. | magainin and pgla are 23- and 21-residue peptides isolated from the skin of the african clawed frog xenopus laevis. they protect the frog from infection and exhibit a broad-spectrum antimicrobial activity in vitro. the mechanism of this activity involves the interaction of magainin with microbial membranes. we have measured the secondary structure and membrane-perturbing ability of these peptides to obtain information about this mechanism. our results show that mgn2a forms a helix with an averag ... | 1990 | 2350550 |
| [an apparatus for dual microelectrode fixation of current in the oocytes of the frog xenopus laevis]. | | 1990 | 2350797 |
| mesoderm induction and the control of gastrulation in xenopus laevis: the roles of fibronectin and integrins. | exposure of isolated xenopus animal pole ectoderm to the xtc mesoderm-inducing factor (xtc-mif) causes the tissue to undergo gastrulation-like movements. in this paper, we take advantage of this observation to investigate the control of various aspects of gastrulation in xenopus. blastomeres derived from induced animal pole regions are able, like marginal zone cells, but unlike control animal pole blastomeres, to spread and migrate on a fibronectin-coated surface. dispersed animal pole cells are ... | 1990 | 2351067 |
| mapping of the presumptive brain regions in the neural plate of xenopus laevis. | two cell autonomous fluorescent labels (dii and hoechst) were used as vital markers in a fate map study of the xenopus neural plate and ridge. most areas of the brain derive from the neural plate in a fate map that is consistent with the topology of a sheet rolling into a tube, i.e., neighboring areas are maintained as neighbors. this has enabled us not only to plot the fates of larval brain structures, but also to suggest their primordial orientation in the neural plate. since overlapping areas ... | 1990 | 2351962 |
| placement of small lipovitellin subunits within the vitellogenin precursor in xenopus laevis. | n-terminal amino acid sequence data for the small lipovitellin subunits in xenopus laevis crystalline yolk platelets indicate that lv2 beta is derived from vitellogenin a2 and that lv2 tau is most likely derived from vitellogenin a1. the small lipovitellin subunits apparently commence within the exon 24 region of the parental vitellogenins, flanking the c-terminal end of phosvitin. as a consequence, we conclude that most of the vitellogenin sequence encoded by exons 30 to 35 is not accounted for ... | 1990 | 2352275 |
| a monoclonal mouse anti-human il-2 receptor antibody (anti-tac) will recognize molecules on the surface of xenopus laevis immunocytes which specifically bind ril-2 and are only slightly larger than the human tac protein. | we have made visible the binding of a mouse monoclonal anti-human interleukin 2 (il-2) receptor (anti-tac) antibody on the surface of phytohemagglutinin (pha)-stimulated xenopus thymocytes using a colloidal gold-conjugated goat anti-mouse antibody and transmission electron microscopy. no binding was found when a different mouse monoclonal antibody (mab) of the same isotype and subclass was tested, or when the anti-tac antibody was omitted from the procedure. after metabolic radiolabeling of the ... | 1990 | 2354864 |
| flanking sequences of xenopus 5 s rna genes determine differential inhibition of transcription by h1 histone in vitro. mitotic phosphorylation of h1 decreases its inhibitory power. | in xenopus laevis chromatin histone h1 selectively inhibits the transcription of oocyte 5 s rna genes while not affecting the transcription of somatic 5 s rna genes (schlissel, m. s., and brown, d. d. (1984) cell 37, 903-913; wolffe, a. p. (1989) embo j. 8, 527-537). to explore possible mechanisms of this specific action of h1 we analyzed the in vitro transcription of h1.dna complexes. we found that the selective inhibitory effect of h1 in this system depends entirely on the flanking sequences o ... | 1990 | 2355019 |
| critical time periods and the effect of tryptophan in malathion-induced developmental defects in xenopus embryos. | xenopus laevis embryos were exposed to the organophosphorus insecticide malathion or its metabolite malaoxon during the first four days of development. the compounds produced the following defects in a dose dependent manner: reduced size, abnormal pigmentation, abnormal gut, enlargement of the atria and aorta, bent notochord and lowered nad+ levels. notochords were bent downward between the third and sixth somites with concurrent compression of the somites. anterior intestine diameter was increa ... | 1990 | 2355801 |
| nucleocytoplasmic transport and processing of small nuclear rna precursors. | we have analyzed the structures and locations of small nuclear rna (snrna) precursors at various stages in their synthesis and maturation. in the nuclei of pulse-labeled xenopus laevis oocytes, we detected snrnas that were longer than their mature forms at their 3' ends by up to 10 nucleotides. analysis of the 5' caps of these rnas and pulse-chase experiments showed that these nuclear snrnas were precursors of the cytoplasmic pre-snrnas that have been observed in the past. synthesis of pre-snrna ... | 1990 | 2355910 |
| rapid and apparently error-prone excision repair of nonreplicating uv-irradiated plasmids in xenopus laevis oocytes. | repair of uv-irradiated plasmid dna microinjected into frog oocytes was measured by two techniques: transformation of repair-deficient (delta uvrb delta reca delta phr) bacteria, and removal of uv endonuclease-sensitive sites (ess). transformation efficiencies relative to unirradiated plasmids were used to estimate the number of lethal lesions; the latter were assumed to be poisson distributed. these estimates were in good agreement with measurements of ess. by both criteria, plasmid dna was eff ... | 1990 | 2355915 |
| cleavage plane determination in amphibian eggs. | in the present study using eggs of cynops pyrrhogaster and xenopus laevis, we examined (1) structural changes in the cytoplasm before the appearance of the cleavage furrow using a cytochemical method, (2) the time of cleavage plane determination depending on the mitotic apparatus (ma), by changing the shape of the eggs, and (3) the time of arrival of the "cleavage stimulus" at the cortex, by injecting colchicine solution or removing cytoplasm. results were as follows: (1) in amphibian eggs the d ... | 1990 | 2356982 |
| the primary structure of rat ribosomal protein s20. | the amino acid sequence of the rat 40 s ribosomal subunit protein s20 was deduced from the sequence of nucleotides in two recombinant cdnas. ribosomal protein s20 has 119 amino acids and has a molecular weight of 13,364. hybridization of the cdna to digests of nuclear dna suggests that there are 16-19 copies of the s20 gene. the mrna for the protein is about 600 nucleotides in length. rat s20 is homologous to xenopus laevis s22 and is related to mycoplasma capricolum s10 and to escherichia coli ... | 1990 | 2357470 |
| synaptic contact between embryonic neurons and acetylcholine receptor-fibroblast. | 1. mouse fibroblast cell lines were established that stably express torpedo californica acetylcholine receptors (achr) on their cell surface in quantities sufficient for biochemical and pharmacological analyses, as well as electrophysiological analysis at the single channel level. 2. surface-expressed achrs were shown to be assembled into proper alpha 2 beta gamma delta pentamers. 3. the distribution of surface-achrs was uniform and identical in every cell. 4. we were able to successfully cocult ... | 1990 | 2359035 |
| cis-acting sequences and trans-acting factors required for constitutive expression of a microinjected hsp70 gene after the midblastula transition of xenopus laevis embryogenesis. | microinjected human hsp70 promoter-chloramphenical acetyl transferase (cat) chimeric genes are constitutively expressed immediately after the midblastula transition of xenopus embryogenesis. analysis of a series of 5'-deletion mutants in the hsp70 promoter revealed that sequences within 74 bases of the transcriptional start site were sufficient for strong basal activity. we investigated the role of specific sequences in the basal promoter by injecting hsp70-cat vectors containing linker-scanner ... | 1990 | 2361336 |
| use of frog embryo teratogenesis assay-xenopus and an exogenous metabolic activation system to evaluate the developmental toxicity of diphenylhydantoin. | the teratogenic potential of diphenylhydantoin (dph) and hydroxylated metabolites (hpph) was evaluated with the frog embryo teratogenesis assay--xenopus (fetax). embryos of the south african clawed frog, xenopus laevis were exposed to dph and hpph in two separate static-renewal experiments with and without the presence of an exogenous metabolic activation system (mas) for 96 hr. two separate dose-response tests were also conducted with dph and hpph with a mas modulated by various mixed functiona ... | 1990 | 2361573 |
| cytoplasmic pools of soluble mrna binding proteins and particles in xenopus laevis early development. | | 1990 | 2362578 |
| three genes under different developmental control encode elongation factor 1-alpha in xenopus laevis. | we have cloned cdnas encoding two variants of the elongation factor for protein synthesis in xenopus laevis, called ef-1 alpha. one of these (42sp50) is expressed exclusively in immature oocytes. it is one of two protein components of a 42s rnp particle that is very abundant in previtellogenic oocytes. the 42s rnp particle consists of various trnas, 5s rna, 42sp50 and a 5s rna binding protein (42sp43). a major function served by 42sp50 appears to be the storage of trnas for later use in oogenesi ... | 1990 | 2362804 |
| phosphorylation of magainin-2 by protein kinase c and inhibition of protein kinase c isozymes by a synthetic analogue of magainin-2-amide. | magainins are a family of antimicrobial peptides present in the skin extracts of xenopus laevis. both magainin-1 and -2 do not have any significant effect on the activity of protein kinase c (pkc). magainin-2 was found to be readily phosphorylated by pkc to 0.5 mol 32p/mol of peptide. neither magainin-1, which has a sequence of s8agk and not s8akk as in the case of magainin-2, nor the magainin-2 analogue with substitution of ala for ser8 was phosphorylated by the kinase, suggesting that ser8 is ... | 1990 | 2365080 |
| effect of denervation on hindlimb regeneration in xenopus laevis larvae. | xenopus laevis larvae at stages 51-57, according to nieuwkoop and faber, were subjected to amputation of the right hindlimb or of both limbs at the thigh or the tarsal level, as well as to somatic denervation of the right limb. larvae at the same stage having undergone amputation of the right limb or of both limbs and sham denervation of the right limb were used as controls. in experimental series i a single denervation of the right limb was performed at the time of amputation. in experimental s ... | 1990 | 2365165 |
| effect of inositol trisphosphate and calcium on oscillating elevations of intracellular calcium in xenopus oocytes. | stimulation of many nonexcitable cells by ca2(+)-mobilizing receptor agonists causes oscillating elevations of the intracellular free ca2+ concentration ((ca2+]i), rather than a continuous increase. it has been proposed that the frequency at which [ca2+]i oscillates determines the biological response. because the occurrence of [ca2+] oscillations is observed together with endogenous inositol polyphosphate (insps) production or following insps application, we injected xenopus laevis oocytes with ... | 1990 | 2365695 |
| removal of 2',3'-dideoxynucleotide residues from injected dna in xenopus laevis oocytes. | dideoxynucleotides have proved to be potent differential inhibitors of dna polymerases in vitro and in vivo. used extensively in studies of dna repair and replication, they have more recently been used as antiviral agents particularly in treating patients for acquired immunodeficiency syndrome (aids). once incorporated, these sugar-modified analogues prevent the further extension of the polynucleotide chain because of the absence of a 3'-hydroxyl group. we demonstrated that, upon injection into ... | 1990 | 2366792 |
| the cell junctions of the notochord of xenopus laevis tadpoles. | the cell junctions of the notochord of xenopus laevis tadpoles were examined with the electron microscope using thin sections, lanthanum tracer experiments, and freeze-fracture replicas. both the peripheral and vacuolated cells of the notochord are connected by numerous spot desmosomes characterized by an intercellular desmogloea and intermediate filaments on the cytoplasmic sides. the peripheral cells also display numerous hemidesmosomes facing the underlying basal lamina. staining with rhodami ... | 1990 | 2368091 |
| transcriptional potentiation of the vitellogenin b1 promoter by a combination of both nucleosome assembly and transcription factors: an in vitro dissection. | the xenopus laevis vitellogenin b1 promoter was assembled into nucleosomes in an oocyte extract. subsequent rna polymerase ii-dependent transcription from these dna templates fully reconstituted in chromatin in a hela nuclear extract was increased 50-fold compared with naked dna. remarkably, under specific conditions, production of a high level of transcripts occurred at very low dna (1 ng/microliter) and hela nuclear protein (1.6 micrograms/microliters) concentrations. when partially reconstitu ... | 1990 | 2370858 |
| the restriction of the heart morphogenetic field in xenopus laevis. | we have examined the spatial restriction of heart-forming potency in xenopus laevis embryos, using an assay system in which explants or explant recombinates are cultured in hanging drops and scored for the formation of a beating heart. at the end of neurulation at stage 20, the heart morphogenetic field, i.e., the area that is capable of heart formation when cultured in isolation, includes anterior ventral and ventrolateral mesoderm. this area of developmental potency does not extend into more p ... | 1990 | 2373257 |
| spreading of trypsinized cells: cytoskeletal dynamics and energy requirements. | the spreading of trypsinized xth-2 cells (a line derived from xenopus laevis tadpole heart endothelia) on glass was investigated. three phases can be distinguished: (1) blebbing of rounded cells, first attachment to a solid substratum and formation of a broad smooth contact area; (2) organization of a peripheral zone of actin fibrils and reinforcement of the basal cytoplasm by a stress fibre-like pattern; (3) extension of lamellae. the first phase seems to be independent of a supply of metabolic ... | 1990 | 2373741 |
| planning the purification process of active cdna in expression cloning strategies. | in principle, it is possible to clone the gene for any receptor that can be expressed in the xenopus laevis frog oocyte and assayed electrophysiologically (e. s. levitan, 1988, tins 11, 41-43). repeated fractionation of a lambda vector cdna library made from mrna which encodes the receptor protein will eventually lead to a single cdna clone. this strategy poses the question as to how large should a lambda vector cdna aliquot be at any fractionation stage in order that one may be relatively certa ... | 1990 | 2374423 |
| nucleotide sequence of a hamster cdna highly homologous to the xenopus laevis s19 ribosomal protein. | | 1990 | 2374723 |
| angiotensin ii-induced calcium mobilization in oocytes by signal transfer through gap junctions. | angiotensin ii (aii) stimulates rapid increases in the concentration of cytosolic calcium in follicular oocytes from xenopus laevis. this calcium response was not present in denuded oocytes, indicating that it is mediated by aii receptors on the adherent follicular cells. the endogenous aii receptors differed in their binding properties from mammalian aii receptors expressed on the oocyte surface after injection of rat adrenal messenger rna. also, the calcium responses to activation of the amphi ... | 1990 | 2374929 |
| the effect of cytochalasin d on protein synthesis in xenopus laevis oocytes. | defolliculated fully grown oocytes of xenopus laevis were treated with cytochalasin d (10 micrograms/ml) and their protein synthesis was studied by labelling with s-35 methionine. this treatment brought about an alteration in pigment pattern as well as a reduction in amino acid uptake by the oocytes. however, the radioactive amino acid taken by cytochalasin-treated oocytes was incorporated into protein in the same proportion as in untreated oocytes. these results suggested that subcortical pigme ... | 1990 | 2375877 |
| comparative studies of carbohydrate-binding proteins from xenopus laevis skin and eggs. sugar-binding specificities and affinity purification. | salt and detergent extracts of acetone-dried powder of xenopus laevis skin and eggs were fractionated on sugar-sepharose columns, to which lactose, melibiose, galactose, rhamnose and mannose had been covalently linked, by successive elution with chelating reagent and specific sugars, resulting in separation of the different ca2(+)-dependent and ca2(+)-independent carbohydrate-binding proteins. the skin of x. laevis contains a salt-extractable ca2(+)-dependent lactose-binding lectin of 30 kilodal ... | 1990 | 2379292 |
| expression of the mammalian system a neutral amino acid transporter in xenopus oocytes. | in this report, we demonstrate the expression of the mammalian system a neutral amino acid transporter in xenopus laevis oocytes following microinjection of mrna from rat liver, chinese hamster ovary (cho) cells, and human placenta. stage 6 oocytes were injected with poly(a+) mrna from one of these three sources and incubated for 24 h prior to assaying na(+)-dependent 2-aminoisobutyric acid transport to monitor the increase in system a activity. the endogenous 2-aminoisobutyric acid uptake rates ... | 1990 | 2380194 |
| cis-acting enhancement of rna polymerase iii gene expression in vitro. | the xenopus laevis s-150 cell-free extract catalyzes in vitro transcription of several rna polymerase iii genes. among these are the xenopus 5s rna gene (somatic type) and the xenopus methionine trna gene. in this report we present an analysis of the transcriptional activity of these two genes either in trans-competition experiments or when the genes are co-localized in the same circular plasmid. in the "cis" arrangement, elevated levels of 5s and trna gene expression are observed, which are dep ... | 1990 | 2381423 |
| identification of a retinoic acid-sensitive period during primary axis formation in xenopus laevis. | retinoic acid (ra) is able to profoundly alter patterning of the primary body axis in embryos of the frog xenopus laevis. the response to ra is dose-dependent, and leads to progressive truncation of the anteroposterior axis, with anterior structures most sensitive. both mesodermal and ectodermal tissues are affected, and in vitro assays demonstrate that induced dorsal ectoderm is one direct target of ra. ra represses expression of anterior-specific genes and concomitantly induces expression of a ... | 1990 | 2384214 |
| studies on cellular adhesion of xenopus laevis melanophores: pigment pattern formation and alteration in vivo by endogenous galactoside-binding lectin or its sugar hapten inhibitor. | we have studied the development of xenopus laevis tail melanophores and the effects on these cells on confrontation with endogenous x. laevis galactoside-binding lectin or its sugar hapten inhibitor thiodigalactoside (tdg). an initial population of unpigmented cells differentiates into melanophores on the dorsal surface of the neural tube, and on the dorsal and ventral apices of the myotomes, forming the larval pattern. melanophores secondarily populate the flank, forming a spaced arrangement wh ... | 1990 | 2385564 |
| expression of the na(+)-k(+)-2cl- cotransporter in xenopus oocytes. | the na(+)-k(+)-2cl- cotransporter (nkcct) is important in mediating net salt transport in a variety of cells. as a first step in obtaining structural information on this transport system, we attempted to express it in xenopus laevis oocytes by injection of poly(a)+ mrna from rat kidney. four days after injection, batches of oocytes were tested for 86rb uptake in presence and absence of 10 microm bumetanide to distinguish that fraction of influx mediated by nkcct. in the absence of bumetanide, th ... | 1990 | 2386212 |
| determination of the sensitive stages for gonadal sex-reversal in xenopus laevis tadpoles. | the response of developing gonads of the clawed toad xenopus laevis tadpoles to estradiol benzoate (eb) was studied between stages 44 and 67 using high resolution techniques. in presumptive genetic males the following results were obtained: 1) 100% sex reversal was induced when eb was administered before translocation of primordial germ cells (pgcs) from the gonadal epithelium into the medullary region (stages 44-50). 2) ambiguous gonads were formed when eb treatment was initiated at stages 51-5 ... | 1990 | 2386730 |
| enhancers for rna polymerase i in mouse ribosomal dna. | the intergenic spacer of the mouse ribosomal genes contains repetitive 140-base-pair (bp) elements which we show are enhancers for rna polymerase i transcription analogous to the 60/81-bp repetitive enhancers (enhancers containing a 60-bp and an 81-bp element) previously characterized from xenopus laevis. in rodent cell transfection assays, the 140-bp repeats stimulated an adjacent mouse polymerase i promoter when located in cis and competed with it when located in trans. remarkably, in frog ooc ... | 1990 | 2388626 |
| structure of xenopus laevis ribosomal protein l32 and its expression during development. | cdna clones for xenopus laevis ribosomal protein l32 have been isolated and sequenced. the deduced amino acid sequence indicates that l32 is a basic protein of 110 amino acids, has a molecular weight of 12,603 and is homologous to the rat ribosomal protein l35. using the cdna clone as a probe to follow the expression of this gene during xenopus development, it has been shown that the pattern of accumulation of this mrna follows the one previously described for other ribosomal protein mrnas durin ... | 1990 | 2388827 |
| uptake and release of 63ni2+ by xenopus embryos during early cleavage stages. | uptake and release of 63ni was studied in dejellied xenopus laevis embryos exposed to 63ni2+ (0.3-30 mumol/l) for 0.5-h intervals during the period 1-4.5 h post-fertilization (i.e. from first cleavage to early blastula stage). at first cleavage, the mean uptake of 63ni by embryos was 12-17 times that by non-fertilized eggs, suggesting that conversion of the vitelline envelope to the fertilization envelope enhanced integumental permeability to 63ni2+. 63ni uptake by embryos at the 1-2-cell stage ... | 1990 | 2390415 |
| interblastomeric plasma membrane formation during cleavage of xenopus laevis embryos. | from comparisons by electron microscopy (em) of organelles isolated by differential centrifugation in sucrose density gradients, and in situ organelles of xenopus cleaving eggs, we propose a sequence of vesicle transformations leading to the formation and completion of interblastomeric membranes: 1) mitochondria located under the extremity of the early groove form bulges which detach to form free vesicles. these vesicles grow by progressive assimilation of the material contained in lipid droplet ... | 1990 | 2390768 |
| early tissue interactions leading to embryonic lens formation in xenopus laevis. | our previous research has demonstrated that lens induction in xenopus laevis requires inductive interactions prior to contact with the optic vesicle, which classically had been thought to be the major lens inductor. the importance of these early interactions has been verified by demonstrating that lens ectoderm is specified by the time it comes into contact with the optic vesicle. it has been argued that the tissues which underlie the presumptive lens ectoderm during gastrulation and neurulation ... | 1990 | 2390999 |
| measurement of histone mrna transcript abundance in xenopus oocytes by a quantitative primer extension assay. | a quantitative primer extension method was used to measure the mass of histone gene transcripts in mature oocytes of the amphibian xenopus laevis. the procedure, using a large excess of gene-specific oligonucleotide primer and continuous incorporation of a radiolabeled deoxynucleoside triphosphate precursor, is more sensitive and quantitative than primer extension assays employing end-labeled primers. it was determined that there are stoichiometric amounts, approximately 2 x 10(8) copies, of mrn ... | 1990 | 2393580 |
| the neuroendocrine polypeptide 7b2 is a precursor protein. | the neuroendocrine protein 7b2 is highly conserved and widely present in neurons and endocrine cells. it is coexpressed with the prohormone proopiomelanocortin (pomc) in the intermediate lobe of the pituitary gland of xenopus laevis. to study the biosynthesis of 7b2 in this amphibian, an anti-7b2 monoclonal antibody was used in immunoprecipitation analysis of newly synthesized radiolabeled proteins, produced by pulse and pulse-chase-incubated neurointermediate lobes. following a 15-min pulse inc ... | 1990 | 2394742 |
| expression of rat liver na+/l-alanine co-transport in xenopus laevis oocytes. effect of glucagon in vivo. | poly(a)+ rna (mrna) isolated from rat liver was injected into xenopus laevis oocytes, and expression of na+/l-alanine transport was assayed by measuring na(+)-dependent uptake of l-[3h]alanine. expression of na+/l-alanine transport was detected 3-7 days after mrna injection, and was due to an increment of the na(+)-dependent component. after injection of 40 ng of total mrna, na(+)-dependent uptake of l-alanine was 2.5-fold higher than in water-injected oocytes. in contrast with na+/l-alanine tra ... | 1990 | 2396979 |
| effect of mutations in domain 2 on the structural organization of oocyte 5 s rrna from xenopus laevis. | in order to test and refine the molecular model of xenopus laevis 5 s rrna proposed in a previous work, we have synthesized, by site-directed mutagenesis and in vitro transcription, four mutants in the internal loop b and in the hairpin loop c of domain 2. the conformations of these mutant 5 s rrnas have been tested using a variety of enzymatic and chemical structure-specific probes and computer modeling. the mutations induce conformational changes restricted to the mutated regions. our results ... | 1990 | 2398495 |
| additional intragenic promoter elements of the xenopus 5s rna genes upstream from the tfiiia-binding site. | the major promoter element of the xenopus laevis 5s rna gene is located within the transcribed region of the gene and forms the binding site for the transcription initiation factor tfiiia. we report an analysis of deletion and substitution mutations within the coding region of the major oocyte-type 5s gene of x. laevis. our results differ from those of previous mutagenesis studies conducted on the somatic-type genes of xenopus borealis and x. laevis. transcription assays in whole oocyte s-150 ex ... | 1990 | 2398887 |
| uptake of biotin by native xenopus laevis oocytes. | the present study examined biotin uptake by xenopus laevis oocytes in vitro. uptake of low (0.03 microm) and high (10 microm) concentrations of biotin was linear with time for up to 4 h of incubation and occurred with little initial binding to oocytes. uptake of biotin was dependent on extracellular na+ concentration [na+]o and was severely inhibited when na+ was replaced by other monovalent cations [choline, tetraethylammonia, li+, and tris(hydroxymethyl)aminomethane]. the initial rate of bioti ... | 1990 | 2399962 |
| the anterior extent of dorsal development of the xenopus embryonic axis depends on the quantity of organizer in the late blastula. | in amphibian gastrulae, the cell population of the organizer region of the marginal zone (mz) establishes morphogenesis and patterning within itself and within surrounding regions of the mz, presumptive neurectoderm, and archenteron roof. we have tested the effects on pattern of reducing the amount of organizer region by recombining halves of xenopus laevis late blastulae cut at different angles from the bilateral plane. when regions within 30 degrees of the dorsal midline are excluded from reco ... | 1990 | 2401200 |
| the 5'-flanking sequence of the loach oocyte 5s rrna gene contains a signal for effective transcription. | deletion mutants of loach oocyte 5s rrna genes were injected and transcribed in vivo in the nuclei of loach (misgurnus fossilis) and xenopus laevis. a control region was found in the 5'-flanking sequence, the elimination of which greatly decreases in vivo transcription of 5s rrna genes. this cis-acting element is located in the region between nt-18 and the transcription start point. we propose that the oocyte nucleus contains (a) specific transcriptional factor(s), ntfo, which interacts with the ... | 1990 | 2401403 |
| the effects of disrupting 5s rna helical structures on the binding of xenopus transcription factor iiia. | block mutations were constructed in helical stems ii, iii, iv and v of xenopus laevis oocyte 5s rna. the affinities of these mutants for binding to transcription factor iiia (tfiiia) were determined using a nitrocellulose filter binding assay. mutations in stems iii and iv had little or no effect on the binding affinity of tfiiia for 5s rna. however, single mutants in stems ii and v (positions 16-21, 57-62, 71-72, and 103-104) which disrupt the double helix, reduce the binding of tfiiia by a fac ... | 1990 | 2402434 |
| functional difference between the sites of ribosomal 40s precursor 3' end formation in xenopus laevis and xenopus borealis. | in the ribosomal genes of x. laevis, the sequence gacttgcnc is found about 60bp upstream of the gene promoter (t3) and is necessary and sufficient to cause termination of rna polymerase i transcription. at the 3' end of the 40s precursor coding region (t2) a sequence differing by one nucleotide, gacttgcng, directs rna 3' end formation but allows polymerase to transcribe on into the intergenic spacer (labhart and reeder, 1989, genes and dev. 4: 269-276). sites corresponding to t2 and t3 are also ... | 1990 | 2402447 |
| xenopus laevis alpha and beta thyroid hormone receptors. | the xenopus laevis genome encodes two genes for the alpha (tr alpha) and two genes for the beta (tr beta) thyroid hormone receptors. the two tr alpha genes closely resemble their rat, human, and chicken counterparts. no alternatively spliced tr alpha cdna clones were found in the 5' untranslated region (5' utr). in contrast, complex alternative splicing of tr beta mrna occurs within the 5' utr as well as possible alternative transcriptional start sites. as many as eight exons encoding mainly the ... | 1990 | 2402492 |
| molecular cloning of androgen receptors from divergent species with a polymerase chain reaction technique: complete cdna sequence of the mouse androgen receptor and isolation of androgen receptor cdna probes from dog, guinea pig and clawed frog. | we have cloned and sequenced 2.8 kilobases of cdna encoding the mouse androgen receptor by rna amplification with transcript sequencing. sequence analysis predicts that this cdna contains an open reading frame of 2697 nucleotides encoding a polypeptide of 899 amino acids. androgen receptor cdna probes of dog, guinea pig, and frog were also isolated and sequenced using consensus primers derived from human and rat androgen receptor cdnas. northern blot analysis with the species-specific probes rev ... | 1990 | 2403358 |
| tagetitoxin: a new inhibitor of eukaryotic transcription by rna polymerase iii. | we demonstrate that tagetitoxin, a bacterial phytotoxin, preferentially inhibits eukaryotic rna polymerase iii. we used promoter-directed transcription of cloned genes in cell-free extracts to compare tagetitoxin inhibition of rna polymerases from diverse sources. in hela cell extracts, accumulation of 5 s rrna, and u6 snrnas (transcribed by rna polymerase iii) was inhibited at 0.3-3.0 microm tagetitoxin but transcription from adenovirus 2 major late promoter (rna polymerase ii) was not signific ... | 1990 | 2403565 |
| diacylglycerol production in xenopus laevis oocytes after microinjection of p21ras proteins is a consequence of activation of phosphatidylcholine metabolism. | microinjection of p21ha-ras proteins into xenopus laevis oocytes induces a rapid increase of 1,2-diacylglycerol (dag) levels. the observed alterations in dag levels were consistent with the ability of the protein to induce maturation, measured by germinal vesicle breakdown (gvbd). both the increase in dag levels and gvbd activity were dependent on the ability of the proteins to undergo membrane translocation. alterations of dag levels or gvbd activity did not correlate with changes in the levels ... | 1990 | 2403640 |
| the recovery of organelle transport and microtubule integrity in myelinated axons that are frozen and thawed. | myelinated axons of xenopus laevis were rapidly frozen in liquid nitrogen and thawed in a potassium glutamate based medium. organelles within isolated, thawed axons were visualized by light microscopy. after thawing, organelles were stationary for about 5 min. following this quiescent period, organelles exhibited a low frequency oscillation in the longitudinal direction of the axon; some of the organelles then began to move in either the anterograde or retrograde directions. electron microscopic ... | 1985 | 2408718 |
| characterization of the rna binding properties of transcription factor iiia of xenopus laevis oocytes. | a nitrocellulose filter binding assay has been developed to study the interaction of xenopus transcription factor iiia with 5s rna. the protein binds xenopus oocyte 5s rna with an association constant of 1.4 x 10(9) m-1 at 0.1 m salt, ph 7.5 at 20 degrees c. tf iiia binds wheat germ 5s rna with a two-fold higher affinity, e. coli 5s rna with a four-fold weaker affinity, and has a barely detectable interaction with yeast trnaphe. the preference for binding eukaryotic 5s rna is enhanced in competi ... | 1985 | 2410862 |
| epidermal keratin gene expressed in embryos of xenopus laevis. | dg81 is a cdna clone derived from a subtracted library containing those rna molecules that are present in gastrulae but absent from eggs of the frog xenopus laevis. dg rnas (where dg indicates differentially expressed in gastrula) represent the products of new transcription activated in the embryo at the midblastula transition or shortly thereafter. dg81 rna is first detected in middle to late gastrulae, peaks in abundance in early tadpoles, and declines to background levels by the end of metamo ... | 1985 | 2410923 |
| the two embryonic u1 rna genes of xenopus laevis have both common and gene-specific transcription signals. | we have cloned and sequenced the 1842-bp repeat dna encoding the two xenopus laevis embryonic u1 rnas, xu1a and xu1b. although these two u1 rnas are almost identical in sequence and are coordinately expressed during early embryogenesis, the flanking sequences of their genes show very little homology. both genes contain two short conserved sequences, centered around positions -55 and +19, that probably are essential for 5' and 3' end formation of u1 rnas, respectively. efficient transcription of ... | 1985 | 2411540 |
| transcription signals in embryonic xenopus laevis u1 rna genes. | a genomic clone of the most abundant u1 rna genes from xenopus laevis was isolated from erythrocyte dna and sequenced. two different u1 rna genes, u1a and u1b, are encoded in an hindiii 1.5-kb fragment and both are expressed after microinjection in xenopus oocytes. deletions and site-directed mutagenesis of the clones revealed two promoter elements in the u1b gene; one, located 250-220 nucleotides upstream from the 5' terminus of mature u1 rna, functions as an activator, yielding a 10-fold promo ... | 1985 | 2411541 |
| a cell surface marker of thymus-dependent lymphocytes in xenopus laevis is identifiable by mouse monoclonal antibody. | a mouse monoclonal antibody (mab), named xt-1 (igg2b,lambda), was prepared against j strain xenopus laevis thymocytes. the determinant recognized by this mab (xt-1 determinant) was expressed by 92-98% thymocytes and 22-37% splenic lymphocytes from intact j strain frogs and larvae, as analyzed by flow cytofluorometry. the xt-1 determinant was also expressed by 20-30% peripheral blood lymphocytes and 5-11% bone marrow lymphocytes from adult, and 11-17% liver lymphocytes from larval j strain xenopu ... | 1985 | 2411573 |
| genes and pseudogenes for rat u3a and u3b small nuclear rna. | we report here the isolation and primary structure of two genes encoding rat u3 small nuclear rna. one of the genes encodes u3b rna; the other encodes an rna which is almost identical to u3a rna. both genes are expressed after microinjection into the nuclei of xenopus laevis oocytes and can direct the accumulation of mature u3 rna as well as longer transcripts which may be the u3 precursors. we have also isolated and sequenced four other regions of the rat genome homologous to u3 rna. one of the ... | 1985 | 2411940 |
| transcription, processing and nuclear transport of a b1 alu rna species complementary to an intron of the murine alpha-fetoprotein gene. | the alu sequence family comprises the major dispersed repeat sequences of rodent and primate genomes, numbering greater than 300,000 copies in the human haploid genome. the function of these elements is unknown. the sequences can be transcribed by rna polymerase iii and represent a substantial fraction of total heterogeneous nuclear rna. alu sequences can be found both in the flanking regions and within the transcription units of several well-characterized genes. here we show that some members o ... | 1985 | 2412135 |
| developmental changes in the pattern of larval beta-globin gene expression in xenopus laevis. identification of two early larval beta-globin mrna sequences. | we have analysed beta-globin mrna sequences in total rna extracted from embryos and tadpoles of xenopus laevis at different stages of development and we have identified the most abundantly transcribed beta-globin mrna (beta t1). the entire nucleotide sequence of a cdna clone corresponding to this mrna is known. we have now identified the gene corresponding to this mrna and we have determined the nucleotide sequences of its immediate 5'-flanking region. using a dna fragment from within the coding ... | 1985 | 2413218 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| altered morphogenesis and its effects on gene activity in xenopus laevis embryos. | | 1985 | 2420514 |
| the secondary structures of the xenopus laevis and human mitochondrial small ribosomal subunit rna are similar. | extensive corrections of the nucleotide sequence of the xenopus laevis mitochondrial small ribosomal subunit rna gene [roe et al. (1985) j. biol. chem. 260, 9759-9774] are reported. we found an additional fragment of 142 nucleotides and describe 25 nucleotide differences scattered in the gene. the nucleotide sequence the same gene of bovine mitochondrion. we propose a new secondary structure for the product of the x. laevis gene. contrary to the finding of roe et al., we observed the same genera ... | 1986 | 2420643 |
| gene expression in xenopus embryogenesis. | this article considers some aspects of the storage of macromolecules in the oocyte of xenopus laevis and the activation of previously unexpressed genes during early embryogenesis. the large quantity and complex nature of poly(a)+ rna accumulated in the egg provides the cleavage embryo with a supply of mrna sufficient to sustain protein synthesis for several hours of development. onset of gene activity at the midblastula transition (mbt) leads to the synthesis and accumulation of molecules of var ... | 1985 | 2420914 |
| sodium entry pathways in renal epithelial cell lines. | na+ entry into kidney epithelial cells occurs by a multiplicity of pathways. established cell lines such as the a6 cells, derived from the collecting duct of the kidney of xenopus laevis, mdck cells, from the distal tubule of a dog kidney, and the llc-pk1 cells, originating from the proximal tubule of a pig kidney, provide excellent model cell systems for the detailed characterization and isolation of the proteins which comprise these entry pathways. major pathways of na+ entry include the amilo ... | 1986 | 2421147 |
| halothane-induced changes in acetylcholine receptor channel kinetics are attenuated by cholesterol. | the single-channel recording technique was used to investigate the role of membrane lipids in the action of general anesthetics on ion channels. we examined the effects of halothane on acetylcholine receptor channels in xenopus laevis myocytes in which the plasma membrane cholesterol level had been changed by pretreatment with cholesterol-rich or cholesterol-free liposomes. we found that the alteration in acetylcholine receptor channel kinetics, elicited in the presence of clinically-relevant co ... | 1986 | 2421772 |
| cytokeratin expression in simple epithelia. ii. cdna cloning and sequence characteristics of bovine cytokeratin a (no. 8). | cytokeratin a (no. 8) is a cytoskeletal protein (mr, approximately 53,000 in bovine cells) which is typical of all simple epithelia, is widespread in all cultured epithelial cells, and together with its partner cytokeratin d, is the first cytokeratin expressed during embryogenesis (synonyms for this protein are endo a and troma-1 antigen). we isolated a clone (pkb8(1] from a puc8 cdna library prepared from poly(a)+-rna of bovine bladder urothelium which contains the 3' nontranslated portion and ... | 1986 | 2422084 |
| genesis and regression of the figures of eberth and occurrence of cytokeratin aggregates in the epidermis of anuran larvae. | in tadpoles of rana temporaria, bufo bufo and xenopus laevis the development of the massive skeins of tonofilaments (cytokeratin intermediate filaments) that form the figures of eberth follows a similar sequence in all species studied. increase in the number of filaments is preceded by increase in polyribosomes and rer in the basal layer cells of the epidermis. a filamentous zone develops proximally in the cells concurrently with hemidesmosomes, which assume the typical larval bobbin form as the ... | 1986 | 2422986 |
| a monoclonal antibody specific for snrnps u1 and u2. | a monoclonal antibody (d-5) is described which selectively precipitates snrnps u1 and u2. the antibody was derived from a mouse immunized with extracts from chick embryonic nuclei. by immunoblotting on either total proteins from purified snrnps u1-u6, u2-u6 or u1 only, we could demonstrate that the monoclonal antibody cross-reacts with the u1 rnp specific polypeptide a and the u2 rnp specific polypeptide b", thereby establishing that the two snrnp proteins share at least one epitope. d-5 precipi ... | 1986 | 2423369 |
| glyceraldehyde-3-phosphate dehydrogenase is a nonhistone protein and a possible activator of transcription in neurons. | a single-stranded dna-binding protein of mr 35,000 (35k protein) was isolated from calf cerebral cortex by affinity chromatography on immobilized double-stranded and single-stranded dna. its localization in the nuclear compartment was demonstrated by immunohistochemistry. previous studies had uncovered a homologous nonhistone chromosomal protein in the nuclei of rat cerebral cortex neurons, cerebellar neurons, oligodendrocytes, and liver cells. the rat protein accumulated in the nuclear compartm ... | 1986 | 2423647 |
| mapping of the displacement loop within the nucleotide sequence of xenopus laevis mitochondrial dna. | the mtdna of the african frog, xenopus laevis, has a triple-stranded displacement loop (d-loop) structure at the origin of heavy strand dna replication. the major species of displacing strands has a length of 1670 nucleotides, approximately 3 times the length of mouse or human d-loop mtdna strands. we report experiments that precisely map the termini of the d-loop strand within a revised sequence of the origin region. analysis of d-loop mtdna strands labeled in vitro at the 5' end using polynucl ... | 1986 | 2424898 |