| 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 |
| patch clamp characterization of sodium channels expressed from rat brain cdna. | sodium currents, ina, were recorded from xenopus laevis oocytes which had been injected with mrna synthesized by in vitro transcription of the rat brain sodium channel ii cdna (noda et al. 1986 a, b). patch pipettes were used to apply depolarizing voltage steps and to record macroscopic sodium currents of between 50 and 750 pa from cell-attached patches of the oocyte membrane. with a combination of whole-cell and patch clamp recording, the properties of the implanted sodium channels could be stu ... | 1987 | 2435540 |
| isolation of mrna from membrane-bound polysomes synthesizing sepia officinalis haemocyanin in xenopus laevis oocytes. | isolation and translation in xenopus laevis oocytes of the mrnas from the nuclear pellet and the cytoplasmic supernatant of the branchial glands from sepia officinalis, homogenized in the presence of vanadyl-ribonucleoside complexes, revealed that the membrane-bound polysomes for haemocyanin sedimented together with the nuclei. centrifugation on a 15-50% sucrose gradient of these polysomes, released by treatment with triton x-100, yielded a major peak of heavy ones. the messenger fraction, isola ... | 1987 | 2436622 |
| gaba receptors induced in xenopus oocytes by chick brain mrna: evaluation of tbps as a use-dependent channel-blocker. | sensitivity to gaba was induced in xenopus laevis oocytes by injection of poly(a)+ mrna extracted from 19-day chick embryo brain. the effect of the convulsant drug t-butylbicyclophosphorothionate (tbps) was studied on the responses to bath-applied gaba using voltage-clamp techniques. tbps reversibly inhibited the gaba-evoked current (igaba) in a dose-dependent manner; however, the chloride currents evoked by carbachol or serotonin, or the spontaneous chloride fluctuations, were unaffected. the o ... | 1987 | 2437999 |
| activation of cryptic promoters of human c-myc genes in microinjected xenopus laevis oocytes. | the human cellular oncogene c-myc contains two promoters at the 5' end of its first non-coding exon. cryptic promoters located within the first intron are also activated to synthesize aberrant c-myc mrnas in some burkitt lymphomas with a t(8: 14) chromosome translocation in which a part of the gene structure, often the 5' non-coding exon, is truncated. we have shown elsewhere that microinjected plasmid dna carrying a normal, intact human c-myc gene directs efficient faithful transcription from i ... | 1987 | 2438422 |
| hormonal activation of ionic currents in follicle-enclosed xenopus oocytes. | membrane currents were recorded, using the voltage clamp technique, from xenopus laevis oocytes still surrounded by their enveloping follicular and epithelial cells. exposure of the follicles to mammalian gonadotropins elicited a current generated largely by an increase in membrane k+ conductance. the gonadotropin response resembled responses elicited by adenosine and catecholamines in the same follicle, but was not blocked by purinergic or catecholaminergic antagonists. the gonadotropin-induced ... | 1987 | 2438692 |
| membrane turnover in rod photoreceptors: ensheathment and phagocytosis of outer segment distal tips by pseudopodia of the retinal pigment epithelium. | we have documented the ultrastructural changes that occur within the photoreceptor outer segment and the retinal pigment epithelium (rpe) during photosensitive membrane turnover. we employed an in vitro eyecup preparation from xenopus laevis in which a large shedding event was induced by adding the excitatory amino acid l-aspartate (greenberger & besharse 1985; j. comp. neurol. 239, 361-372). we found that during l-aspartate-induced shedding the rpe cells formed, on their apical domains, previou ... | 1987 | 2438704 |
| expression of an omega-conotoxin-sensitive calcium channel in xenopus oocytes injected with mrna from torpedo electric lobe. | xenopus laevis oocytes were injected with poly(a)+ rna isolated from the electric lobe of torpedo californica. six to nine days after mrna injection of the oocytes a cadmium-sensitive inward current could be detected in oocytes bathed in a calcium- and chloride-free solution containing 40 mm barium. this inward current could be distinguished from the native barium current of control oocytes by its high sensitivity to blockade by cadmium ions and its inhibition by omega-conotoxin, a peptide neuro ... | 1987 | 2440049 |
| neurotensin and acetylcholine evoke common responses in frog oocytes injected with rat brain messenger ribonucleic acid. | 1. the intracellular reaction mechanism underlying electrophysiological responses evoked by neurotensin (nt) was studied using xenopus laevis oocytes injected with poly (a)+ messenger ribonucleic acid (mrna) isolated from rat brains. 2. a few days after the injection of mrna, oocytes were found to acquire sensitivity to nt and substance p. 3. under voltage-clamp conditions (-60 mv), application of nt to mrna-injected oocytes produced transient and oscillatory inward currents which began after a ... | 1987 | 2442367 |
| further characterization of the slow muscarinic responses in xenopus oocytes. | in immature follicular oocytes of the frog xenopus laevis, application of muscarinic agonists evokes a complex response consisting of a fast and a slow cl currents (the dominant responses), cl current fluctuations, and a less prominent slow k current. the characteristics of the slow ach-evoked potassium current were studied using the two-electrode voltage clamp method, and compared to those of the ach-evoked cl currents. in experiments designed to study the k current response separately, without ... | 1987 | 2442712 |
| both barium and calcium activate neuronal potassium currents. | amphibian spinal neurons in culture possess both rapidly inactivating and sustained calcium-dependent potassium current components, similar to those described for other cells. divalent cation-dependent whole-cell outward currents were isolated by subtracting the voltage-dependent potassium currents recorded from xenopus laevis neurons in the presence of impermeant cadmium (100-500 microm) from the currents produced without cadmium but in the presence of permeant divalent cations (50-100 microm). ... | 1987 | 2442762 |
| inositol trisphosphate activates a voltage-dependent calcium influx in xenopus oocytes. | injection of inositol trisphosphate (ip3) into oocytes of xenopus laevis induces the appearance of a transient inward (tin) current on hyperpolarization of the membrane. this current is carried largely by chloride ions, but is shown to depend on extracellular calcium, because it is abolished by removal of calcium in the bathing fluid or by addition of manganese. recordings with aequorin as an intracellular calcium indicator show that a calcium influx is activated by hyperpolarization after intra ... | 1987 | 2442764 |
| changes in axonal transport and glial proteins during optic nerve regeneration in xenopus laevis. | | 1987 | 2443306 |
| polar asymmetry in the organization of the cortical cytokeratin system of xenopus laevis oocytes and embryos. | we have used whole-mount immunofluorescence microscopy of late-stage xenopus laevis oocytes and early embryos to examine the organization of their cortical cytokeratin systems. in both mature oocytes and early embryos, there is a distinct animal-vegetal polarity in cytokeratin organization. in mature (stage-vi) oocytes, the cytokeratin filaments of the vegetal region form a unique, almost geodesic network; in the animal region, cytokeratin organization appears much more variable and irregular. i ... | 1987 | 2443336 |
| distribution, expression and germ line transmission of exogenous dna sequences following microinjection into xenopus laevis eggs. | we analysed the fate, expression and germ line transmission of exogenous dna which was microinjected into fertilized eggs of xenopus laevis. dna was injected into fertilized eggs within 1 h following fertilization. the injected dna was dispersed around the site of injection and became localized to cleavage nuclei by stage 6. injected dna persisted in the tissues of 6- to 8-month-old frogs and exhibited a mosaic pattern of distribution with regard to the presence or absence and copy number betwee ... | 1987 | 2443337 |
| expression of xenopus n-cam rna in ectoderm is an early response to neural induction. | we have isolated xenopus laevis n-cam cdna clones and used these to study the expression of n-cam rna during neural induction. the results show that the first marked increase in n-cam rna levels occurs during gastrulation when mesoderm comes in contact with ectoderm and induces neural development. in situ hybridization results show that the early expression of n-cam rna is localized to the neural plate and its later expression is confined to the neural tube. induction experiments with explanted ... | 1987 | 2443340 |
| synthesis of heterogeneous mrna-like rna and low-molecular-weight rna before the midblastula transition in embryos of xenopus laevis. | it has been proposed and is now widely accepted that in xenopus laevis embryogenesis rna synthesis starts only at and after 12 rounds of cleavage, at the time of the midblastula transition (mbt). in this report, however, we provide evidence that rna synthesis takes place prior to the mbt stage in normally developing xenopus embryos. in the present experiments, we cultured fertilized eggs in 80 mm phosphate buffer and loosened the adhesion between blastomeres, so that [3h]uridine could be incorpo ... | 1987 | 2443406 |
| structure and transcription termination of a lysine trna gene from xenopus laevis. | termination of rna polymerase iii transcripts commonly occurs at clusters of t residues. a t4 tract located 72 base-pairs beyond a lysine trna gene from xenopus laevis serves as an efficient termination site for the trna(lys) precursors synthesized from this gene in homologous cell-free extracts. nucleotides following this t tract influence the extent of read-through transcription in vitro, but in a way that differs from xenopus 5 s rna termination. only approximately 50% of the transcripts init ... | 1987 | 2443712 |
| expression of single calcium channels in xenopus oocytes after injection of mrna from rat heart. | oocytes of xenopus laevis, after microinjection with mrna from rat heart, display typical high-threshold calcium (ca) whole cell currents. to prepare to study structure-function relationships of the cardiac ca channel molecule, we examined the fidelity of expression of biophysical and pharmacological properties at the molecular level. cell-attached gigaseal recordings in five k-depolarized oocytes injected with adult rat heart mrna showed single channel ba currents with mean amplitude 1.3-1.5 pa ... | 1987 | 2444117 |
| dopamine mediates the light-evoked suppression of serotonin n-acetyltransferase activity in retina. | the possible role of dopamine in the light-induced suppression of serotonin n-acetyltransferase (nat) activity in retinas of the african clawed frog (xenopus laevis) was investigated using an in vitro eye cup preparation. the nocturnal increase of retinal nat activity was significantly inhibited by either light exposure or exogenous dopamine. spiperone, a dopamine receptor blocker, antagonized this inhibitory effect of light on nat activity, but had no effect in darkness. the effect of spiperone ... | 1987 | 2445415 |
| analysis of cytokeratin domains by cloning and expression of intact and deleted polypeptides in escherichia coli. | using recombination of an appropriate expression vector system (pindu) with a complete cdna encoding a basic (type ii) cytokeratin, i.e. cytokeratin 8 (1) of xenopus laevis, we transformed escherichia coli cells to synthesize considerable amounts of an insoluble eukaryotic cytoskeletal protein. the cytokeratin was deposited in large 'inclusion bodies' in the bacterial cytoplasm but did not form detectable filamentous structures. however, when the e. coli-expressed cytokeratin was purified and co ... | 1987 | 2445561 |
| cell-type-specific expression of epidermal cytokeratin genes during gastrulation of xenopus laevis. | analysis of the spatial pattern of expression of embryo-specific epidermal cytokeratin genes in xenopus laevis shows earliest activity in the animal pole cells of stage-9 blastulae. these genes are transcribed predominantly in the epithelial or outer ectoderm, to a lesser extent in the sensorial or inner ectoderm, and at low levels if at all in other regions of the embryo. in the early gastrula the entire ectoderm, including preneural and preepidermal regions, expresses cytokeratin mrnas; accumu ... | 1987 | 2445625 |
| differential transcription of xenopus oocyte and somatic-type 5 s genes in a xenopus oocyte extract. | we have measured the transcription of xenopus laevis oocyte and somatic-type 5 s rna genes in s-150 extracts prepared from ovaries of mature x. laevis females (glikin, g. c., ruberti, i., and worcel, a. (1984) cell 37, 33-41). we find that somatic-type 5 s genes are transcribed at least 40-fold more efficiently than oocyte-type 5 s genes. since adenovirus va, xenopus oax, and xenopus trnamet genes are all transcribed at levels similar to that of the somatic-type 5 s gene, this difference reflect ... | 1987 | 2445754 |
| properties of single sodium channels translated by xenopus oocytes after injection with messenger ribonucleic acid. | 1. the properties of fast transient na channels induced in the xenopus laevis oocyte plasma membrane after injection of the oocyte with foreign messenger ribonucleic acid (mrna) were investigated with the whole-cell voltage clamp and with the patch-clamp technique. 2. the time course of expression and the effect of the metabolic inhibitors actinomycin d and tunicamycin were studied. the rate of channel insertion reached a maximum only about 3 days after injection with mrna and corresponded to th ... | 1987 | 2445971 |
| dna-binding fingers encoded by a trypanosome retroposon. | a trypanosoma brucei repeated dna element (trs-1, for trypanosome repeated sequence), which seems transposable, may encode a 1651 amino acid polypeptide showing homology with reverse transcriptase. this polypeptide would also carry a dna-binding domain, as suggested by the presence of five dna-binding "fingers" homologous to those of the transcription factor tfiiia of xenopus laevis and retroviral dna-binding proteins. | 1987 | 2445994 |
| effects of veratridine on single neuronal sodium channels expressed in xenopus oocytes. | (1) chick neuronal na+ channels were expressed in xenopus laevis oocytes after injection with total messenger ribonucleic acid (mrna) isolated from chick brain. the currents were investigated with the whole cell voltage clamp and with the patch clamp technique. activation and inactivation of the induced current, and its sensitivity towards tetrodotoxin (ttx) and veratridine were reminiscent of vertebrate neuronal na+ channels. (2) in the presence of veratridine normal single channel openings oft ... | 1987 | 2446243 |
| chloride-thiocyanate interactions in frog muscle anion-conducting channels at ph 5. | bi-ionic membrane potential measurements and three-microelectrode voltage clamp experiments have been performed on surface fibres of xenopus laevis sartorius muscle at various mole fractions of scn- in cl- in the perfusate, at ph 5. potassium was replaced in the test solutions by rubidium and/or tetraethylammonium and when the mole fraction of anions was changed the measured membrane potential changed to a new constant (i.e. time-independent) value. over a mole fraction range of 0.05-0.95 the pe ... | 1987 | 2446245 |
| injection of inositol 1,3,4,5-tetrakisphosphate into xenopus oocytes generates a chloride current dependent upon intracellular calcium. | injection of inositol 1,3,4,5-tetrakisphosphate (ins(1,3,4,5)p4) into voltage-clamped oocytes of xenopus laevis elicited an oscillatory chloride membrane current. this response did not depend upon extracellular calcium, because it could be produced in calcium-free solution and after addition of cobalt to block calcium channels in the surface membrane. however, it was abolished after intracellular loading with the calcium chelating agent egta, indicating a dependence upon intracellular calcium. t ... | 1987 | 2446333 |
| reversible inhibition of protein import into the nucleus by wheat germ agglutinin injected into cultured cells. | the importance of glycoproteins located in the nuclear envelope in nuclear transport was tested by microinjection of karyophilic proteins into the cytoplasm of cultured human cells together with various lectins. wheat germ agglutinin (wga) blocked the nuclear transport of nucleoplasmin, a nuclear protein of xenopus laevis oocytes, and of nonnuclear proteins conjugated with a synthetic peptide containing the nuclear localization signal sequence for simian virus 40 (sv40) large t antigen. its inhi ... | 1987 | 2446896 |
| rate of degradation of [alpha]- and [beta]-oligodeoxynucleotides in xenopus oocytes. implications for anti-messenger strategies. | end-labelled oligodeoxynucleotides were injected into xenopus laevis oocytes and their degradation products were analysed by high-performance ion-exchange liquid chromatography after various times of incubation. the oligonucleotides were synthesised with either the natural [beta] anomers or the synthetic [alpha] anomers of deoxynucleotide units. oligo-[beta] deoxynucleotides are short-lived inside oocytes (half-life approximately equal to 10 min). covalent attachment of an intercalating agent to ... | 1987 | 2447563 |
| membrane currents elicited by porcine vasoactive intestinal peptide (vip) in follicle-enclosed xenopus oocytes. | membrane currents were recorded from voltage-clamped xenopus laevis oocytes, surrounded by their enveloping follicular and epithelial cells. porcine vasoactive intestinal peptide (vip) generated a membrane current due to an increase in membrane conductance to k+. the vip current was mimicked by the adenylate cyclase activator forskolin and was potentiated by phosphodiesterase inhibitors, suggesting that adenosine 3',5'-cyclic monophosphate (cyclic amp) plays a role in mediating the response. tho ... | 1987 | 2447588 |
| the accumulation of mature rna for the xenopus laevis ribosomal protein l1 is controlled at the level of splicing and turnover of the precursor rna. | a specific control regulates, at the level of rna splicing, the expression of the l1 ribosomal protein gene in xenopus laevis. under particular conditions, which can be summarized as an excess of free l1 protein, a precursor rna which still contains two of the nine introns of the l1 gene accumulates. in addition to the splicing block the two intron regions undergo specific endonucleolytic cleavages which produce abortive truncated molecules. the accumulation of mature l1 rna therefore results fr ... | 1987 | 2448138 |
| thyroid hormone induction of keratin genes: a two-step activation of gene expression during development. | to determine the mechanism of action of the thyroid hormone triiodothyronine (t3) during metamorphosis of the amphibian epidermis, we have investigated the developmental activation of the 63-kd keratin genes in the frog xenopus laevis. these genes code for three closely related keratins that first appear in the larval epidermis and accumulate during metamorphosis to become the most abundant proteins in the adult epidermis. we report here that the 63-kd keratins and their mrnas first appear at st ... | 1987 | 2448186 |
| receptors for neuropeptides are induced by exogenous poly(a)+ rna in oocytes from xenopus laevis. | receptors for the hormones vasopressin, angiotensin ii, and thyrotropin-releasing hormone have been studied electrophysiologically in xenopus laevis oocytes previously injected with poly(a)+ rna from the respective receptor-containing tissues. the injected oocytes responded to the hormones by demonstrating oscillations in membrane currents as recorded by the voltage-clamp method. the response was dependent on the hormone concentrations and detectable between 5 and 1000 nm concentrations. size fr ... | 1988 | 2448781 |
| expression of rat brain excitatory amino acid receptors in xenopus oocytes. | xenopus laevis oocytes when injected with rat brain mrna synthesize neuronal receptors that can be analyzed electrophysiologically. after a post-injection incubation period of 24-72 hours, l-glutamic acid, kainic acid and quisqualic acid caused a dose dependent (10-100 microm) depolarization of the oocyte membrane. the voltage and conductance changes associated with kainate activation were distinguishable from those seen for l-glutamate or quisqualate. there was no response to l-aspartate applic ... | 1987 | 2449049 |
| the use of xenopus oocytes for the study of ion channels. | recently, in addition to the "traditional" research on meiotic reinitiation and fertilization mechanisms, the oocytes of the african frog xenopus laevis have been exploited for the study of numerous aspects of ion channel function and regulation, such as the properties of several endogenous voltage-dependent channels and the involvement of second messengers in mediation of neurotransmitter-evoked membrane responses. in addition, injection of these cells with exogenous messenger rna results in pr ... | 1987 | 2449311 |
| tetrodotoxin-sensitive sodium current in native xenopus oocytes. | depolarization of oocytes of xenopus laevis usually elicits mainly passive currents, and a calcium-dependent chloride current. however, oocytes obtained from some donors show, in addition, a transient inward current on depolarization to potentials beyond ca. -40 mv. this current is abolished by tetrodotoxin at submicromolar concentrations, and is prolonged by veratrine; thus, it probably arises through sodium channels of a type similar to those found in nerve and muscle cells. however, the kinet ... | 1987 | 2449697 |
| calcium-dependent events at fertilization of the frog egg: injection of a calcium buffer blocks ion channel opening, exocytosis, and formation of pronuclei. | eggs of xenopus laevis were injected with a calcium buffer before insemination, to examine the effect of preventing or suppressing the sperm-induced increase in intracellular calcium on the fertilization potential, exocytosis, and pronuclear formation. microinjection of bapta [(1,2-bis(o-aminophenoxy)ethane-n,n,n',n'-tetraacetic acid)] at concentrations between 0.2 and 0.7 mm usually suppressed the fertilization potential to a series of transient depolarizations. the fertilization potential was ... | 1988 | 2450795 |
| a detailed model of the three-dimensional structure of escherichia coli 16 s ribosomal rna in situ in the 30 s subunit. | a large body of intra-rna and rna-protein crosslinking data, obtained in this laboratory, was used to fold the phylogenetically and experimentally established secondary structure of escherichia coli 16 s rna into a three-dimensional model. all the crosslinks were induced in intact 30 s subunits (or in some cases in growing e. coli cells), and the sites of crosslinking were precisely localized on the rna by oligonucleotide analysis. the rna-protein crosslinking data (including 28 sites, and invol ... | 1988 | 2451022 |
| 5'-flanking and 5'-proximal exon regions of the two xenopus albumin genes. deletion analysis of constitutive promoter function. | the 5'-flanking regions and the first two exons of the 68kd and 74kd albumin genes of xenopus laevis reveal extensive sequence homology between the two in the exon part, in the 5'-flanking region up to position -400 as well as in the first intron. sequence comparisons of the xenopus genes with either the albumin genes of the chicken and mammals or the mammalian alpha-fetoprotein genes reveals no homology in the 5'-flanking region but some conserved features in the first exon. the analysis of the ... | 1988 | 2451026 |
| amino acid sequence of heavy chain from xenopus laevis igm deduced from cdna sequence: implications for evolution of immunoglobulin domains. | present understanding of the evolution of immunoglobulins is derived almost entirely from studies of a few mammalian species. to obtain information about immunoglobulin genes in xenopus laevis, a cdna library was prepared in the expression vector lambda gt11 from mitogen-stimulated splenocytes of this species. of approximately equal to 50,000 clones screened, 18 were found to express igm epitopes. one of these, lambda xig14, hybridized with rna of rna of approximately equal to 2 kilobases from s ... | 1988 | 2451244 |
| induction of mesodermal tissues by acidic and basic heparin binding growth factors. | the inducing activity of two heparin binding growth factors hbgf-1 (prostate epithelial cell growth factor; acidic pi) and hbgf-2 (fibroblast growth factor; basic pi) from bovine brain has been tested on totipotent ectoderm from early amphibian (xenopus laevis, ambystoma mexicanum) embryos. both factors induced, at high concentrations, mostly compact spheres surrounded by a non-epidermal epithelium. when the concentration or time of incubation was reduced, large muscle inductions frequently orga ... | 1988 | 2451566 |
| stimulation of rna and protein synthesis by intracellular insulin. | like insulin-sensitive somatic cells, stage iv oocytes from xenopus laevis increase their synthesis of rna, protein, and glycogen in response to extracellular insulin. synthesis of rna and protein are also increased when oocytes are maintained under paraffin oil and insulin is microinjected into the cytoplasm. the effects of external and intracellular insulin are additive, suggesting separate mechanisms of action. experiments with nuclei isolated under oil show that rna synthesis can be stimulat ... | 1988 | 2451860 |
| soluble cytokeratins in xenopus laevis oocytes and eggs. | xenopus oocytes contain a radial network of cytokeratins which seems to fragment during meiosis reinitiation (maturation). the mature egg contains only a cortical network of cytokeratins. we have looked for the presence of soluble cytokeratins in oocytes and unfertilized eggs and have found them in both cases. however, the proportion of soluble to insoluble cytokeratins is slightly higher in the egg than in the oocyte. soluble cytokeratins incorporate 35s-methionine at a high rate in the oocyte ... | 1987 | 2451957 |
| mapping of neural crest pathways in xenopus laevis using inter- and intra-specific cell markers. | this study examines the pathways of migration followed by neural crest cells in xenopus embryos using two recently described cell marking techniques. the first is an interspecific chimera created by grafting xenopus borealis cells into xenopus laevis hosts. the cells of these closely related species can be distinguished by their nuclear dimorphism. the second type of marker is created by microinjection of lysinated dextrans into fertilized eggs which can then be used for intraspecific grafting. ... | 1988 | 2452101 |
| localization of kinesin in cultured cells. | kinesin was isolated from bovine brain and used to elicit polyclonal antibodies in rabbits. the specificities of the resulting antibodies were evaluated by immunoblotting. antibodies purified from these sera by their affinity for brain kinesin react with a polypeptide of approximately 120 kd in extracts from bovine brain, ptk1 cells, and mouse neuroblastoma cells. they bind to a pair of polypeptides of approximately 120 kd present in crude kinesin prepared from xenopus eggs and with a single pol ... | 1988 | 2452169 |
| the production of active human thyroid-stimulating hormone from alpha and beta mrnas in xenopus laevis oocytes. | active human thyroid-stimulating hormone (htsh) was produced by xenopus laevis oocytes following injection of an mrna mixture of htsh beta and alpha subunits synthesized by t3 rna polymerase. some of the htsh molecules were secreted into the medium, while others remained in the cells. the active molecules consisted of alpha and beta subunits and were in highly glycosylated form. the xenopus laevis oocyte-produced htsh stimulated the rat thyroid cell line frtl-5 to produce and secrete the cyclic ... | 1988 | 2452635 |
| cytokeratins in certain endothelial and smooth muscle cells of two taxonomically distant vertebrate species, xenopus laevis and man. | using immunolocalization techniques, electron microscopy, and gel electrophoresis combined with immunoblotting, we have noted remarkable interspecies differences in the expression of cytokeratins in certain nonepithelial cells. in the present study we describe, in two taxonomically distant vertebrate species, the african clawed toad xenopus laevis and man, endothelial and smooth muscle cells which express cytokeratin intermediate filaments (ifs), in addition to vimentin and/or desmin ifs. in xen ... | 1987 | 2452760 |
| expression of mrna of beta 1- and beta 2-adrenergic receptors in xenopus oocytes results from structurally distinct receptor mrnas. | poly(a)+-selected rna prepared from cells or tissues that express a homogeneous population of either beta 1- or beta 2-adrenergic receptors was isolated and then microinjected into xenopus laevis oocytes. following microinjection, the expression of beta-adrenergic receptors was assessed by equilibrium radioligand binding analysis using the antagonist ligand [3h]dihydroalprenolol. the pharmacology of the newly- expressed beta-adrenergic receptors in oocyte membranes was the same as that of the or ... | 1988 | 2454228 |
| a calcium-independent chloride current activated by hyperpolarization in xenopus oocytes. | hyperpolarization of oocytes of xenopus laevis usually elicits mainly passive currents. however, when polarized to potentials more negative than about -100 mv, oocytes obtained from some donors show a relatively well maintained current that is carried mainly by chloride ions. this response does not depend upon external calcium, and is thus clearly different from the calcium-dependent transient chloride current previously described. | 1988 | 2454476 |
| changes in heat shock protein synthesis and hsp70 gene transcription during erythropoiesis of xenopus laevis. | as erythroid cells of xenopus laevis differentiate, their capacity for transcription and protein synthesis becomes progressively restricted. mature erythrocytes are thought to be transcriptionally inert and have very low levels of protein synthesis (maclean et al., 1973, cell differ. 2, 261-269). we have examined actual and potential synthetic activity during erythropoiesis by comparing the patterns of protein synthesis and measuring the transcriptional activity of selected genes under ambient a ... | 1988 | 2454851 |
| the first cleavage plane and the embryonic axis are determined by separate mechanisms in xenopus laevis. i. independence in undisturbed embryos. | we examined the spatial relationships between the meridian of sperm entry the plane of first cleavage, and the embryonic axis (defined by the neural groove) in eggs of xenopus laevis. direct measurement of the angular separations between these embryonic structures in gelatin-embedded eggs confirmed the classical conclusion that the sperm entry point and neural groove tend to form on opposite sides of the egg, and also revealed that the first cleavage plane has a nearly random orientation with re ... | 1988 | 2454855 |
| inhibition of rna synthesis in embryo of xenopus laevis by protease inhibitor. | we have studied the role of proteases during the development of xenopus laevis embryos with the aid of protease inhibitors. the activity of proteases was found to be only minimal in the unfertilized egg and during the initiation of development, but activity began to increase at the morula stage. when the activity of proteases was inhibited by antipain, an inhibitor of endopeptidase activity, rna synthesis in the embryo was inhibited. to examine the relationship between the inhibitory effect of a ... | 1988 | 2455764 |
| purification of xenopus laevis mitochondrial rna polymerase and identification of a dissociable factor required for specific transcription. | the xenopus laevis mitochondrial rna (mtrna) polymerase was purified to near homogeneity with an overall yield approaching 50%. the major polypeptides in the final fraction were a doublet of proteins of approximately 140 kilodaltons that copurified with the mtrna polymerase activity. it appeared likely that the smaller polypeptide is a breakdown product of the larger one. the highly purified polymerase was active in nonspecific transcription but required a dissociable factor for specific transcr ... | 1988 | 2457154 |
| intercellular communication in the eight-cell stage of xenopus laevis development: a study using dye coupling. | we report an investigation of dye coupling in the eight-cell stage of xenopus laevis development. our results indicate that fluorophors injected into micrometers at this stage pass only to sister cells (the corresponding macromeres) and that detectable dye transfer occurs only via cytoplasmic bridges, which persist for about the first two-thirds of the fourth cell cycle. we had previously shown that the dorsoventral polarity of the xenopus embryo is regulated by a cell interaction that occurs at ... | 1988 | 2457526 |
| transient potassium current in native xenopus oocytes. | depolarization of follicle-enclosed oocytes of xenopus laevis obtained from some donors elicits, in addition to other responses, a fast transient outward current. after holding the membrane potential at -100 mv this response begins to be activated by depolarizations to around -30 mv, and increases progressively as the voltage is raised further. a striking characteristic is that the current recovers only slowly (several seconds) from inactivation following a depolarizing pulse. because of its out ... | 1988 | 2457925 |
| the distribution of tenascin coincides with pathways of neural crest cell migration. | the distribution of the extracellular matrix (ecm) glycoprotein, tenascin, has been compared with that of fibronectin in neural crest migration pathways of xenopus laevis, quail and rat embryos. in all species studied, the distribution of tenascin, examined by immunohistochemistry, was more closely correlated with pathways of migration than that of fibronectin, which is known to be important for neural crest migration. in xenopus laevis embryos, anti-tenascin stained the dorsal fin matrix and ec ... | 1988 | 2458221 |
| vectors for in vitro synthesis of poly(a)+rna transcripts. | an rna expression plasmid containing a maize zein storage protein gene was modified by the addition of an oligodeoxynucleotide duplex containing oligo(a30) in the rna sense strand to the 3' flank of the gene. by linearizing the plasmid at either side of the oligo(a) region, transcripts with or without a poly(a) tail may be synthesized. poly(a) addition dramatically increases the translation of sp6-transcribed zein transcripts in xenopus laevis oocytes. we describe a derivative of psp64, psp64a, ... | 1988 | 2458300 |
| immunocytochemical and morphological evidence for a retinopetal projection in anuran amphibians. | the centrifugal projection to the retina in anuran amphibians (rana catesbeiana and xenopus laevis) has been investigated by immunocytochemistry, hrp transport, and optic nerve lesionings. fmrfamide- and n-terminal substance p-immunoreactive (fa-ir and sp(3-7)-ir) fibers were abundant in the normal retina and optic nerve but almost absent distal to an optic nerve section or crush after 7-14 days survival. fa-ir and sp(3-7)-ir fibers were traced to the optic nerve from the lamina terminalis (or t ... | 1988 | 2458396 |
| stability of rna in developing xenopus embryos and identification of a destabilizing sequence in tfiiia messenger rna. | synthetic capped rna transcripts injected into fertilized eggs of xenopus laevis have a half-life of 3-4 h. addition of a long (approximately 200 nucleotide) poly(a) tail increases the half-life to 6-8 h which approaches the half-life of natural polyadenylated globin rna injected into embryos. since exonucleolytic action alone could account for the degradation of rna, we tested whether circular rna is stable after injection and find that circles are exceptionally stable (half-life greater than 4 ... | 1988 | 2458900 |
| amino acid sequence microheterogeneities of a type i cytokeratin of mr 51,000 from xenopus laevis epidermis. | the complete cdna-derived sequence of a type i cytokeratin (designated no. 3) from xenopus laevis skin is described. the deduced protein has an mr of 51,888 and consists of a glycine-rich head domain, a well-conserved alpha-helical region and a tail rich in hydroxyamino acid residues. various cdna clones encoding two different mrnas were isolated that differed by short deletions/insertions and point mutations. these microheterogeneities are mainly located in a 'hypervariable region' at the c-ter ... | 1988 | 2458965 |
| rings of negatively charged amino acids determine the acetylcholine receptor channel conductance. | the structure-function relationship of the nicotinic acetylcholine receptor (achr) has been effectively studied by the combination of complementary dna manipulation and single-channel current analysis. previous work with chimaeras between the torpedo californica and bovine achr delta-subunits has shown that the region comprising the hydrophobic segment m2 and its vicinity contains an important determinant of the rate of ion transport through the achr channel. it has also been suggested that this ... | 1988 | 2459620 |
| immunocytochemical identification of non-neuronal intermediate filament proteins in the developing xenopus laevis nervous system. | intermediate filament proteins in the postmetamorphic xenopus laevis nervous system were identified by their crossreactivities on western blots with a pan-specific intermediate filament antibody (anti-ifa). these intermediate filament protein bands on western blots were characterized as 3 cytokeratin-like proteins (49, 55, and 58 kda), one vimentin-like protein (53 kda), two distinct glial fibrillary acidic protein (gfap)-like proteins (60 and 67 kda), and 3 neurofilament proteins (73, 175, and ... | 1988 | 2460198 |
| expression and electrophysiological identification of the receptor for bombesin and gastrin-releasing peptide in xenopus laevis oocytes injected with polya+ rna from rat brain. | the receptor for bombesin and the related peptide, gastrin-releasing peptide (grp) has been induced in frog oocytes by injection of polya+ rna from rat brain. the primed oocytes responded to peptides of the bombesin family (grp, neuromedin c of bombesin) by showing dose-dependent oscillations in membrane currents as recorded by the voltage-clamp method. the induced membrane changes were suppressed when oocytes were pretreated with a bombesin-receptor antagonist. | 1988 | 2460369 |
| [isolation and study of polyadenylated rna from bacillus intermedius]. | a poly(a)+rna fraction was isolated from the overall rna of bacillus intermedius using chromatography on poly(u) sepharose and was shown to be electrophoretically heterogeneous. the presence of a polyadenylate segment was confirmed by hybridization with polyuridine. the biological activity of the poly(a)+rna was proved by the translation in xenopus laevis oocytes. the dynamics of poly(a)+rna synthesis was studied in the course of b. intermedius growth and the content of poly(a)+rna was assayed i ... | 1988 | 2460725 |
| pathway of b1-alu expression in microinjected oocytes: xenopus laevis proteins associated with nuclear precursor and processed cytoplasmic rnas. | we have previously characterized b1-alu gene expression by microinjected xenopus laevis oocytes. the transcription, endonucleolytic processing and its kinetics, nuclear transport kinetics, and subsequent cellular compartmentalization have been described previously (adeniyi-jones and zasloff, nature 317:81-84, 1985). briefly, a b1-alu gene is transcribed by rna polymerase iii to a 210-nucleotide (210nt) primary transcript which is processed to yield 135nt and 75nt rnas. after processing, the 135n ... | 1988 | 2460743 |
| activity of a cloned xenopus albumin gene promoter in the homologous frog oocyte system. | the activity of the liver-specific promoter from the xenopus laevis 68 kda albumin gene in homologous oocytes has been analysed by microinjection. we find that the albumin promoter functions relatively efficiently in oocytes, directing the synthesis of correctly initiated transcripts, and deletion analysis reveals that only a small amount of upstream sequence is required for full activity. | 1988 | 2461224 |
| a possible maternal-effect mutant of xenopus laevis: ii. studies of rna synthesis in dissociated embryonic cells. | embryos from a female of xenopus laevis (designated as no. 65) arrest development at gastrulation and are assumed to be ova-deficient mutant. we dissociated these embryos and studied rna synthesis at different stages. the cells from the ova-deficient embryos reaggregated quite actively as wild-type embryo cells until the late gastrula stage. rna synthesis was normal at the early blastula stage but greatly inhibited by the late blastula (stage 9.5) stage, when the synthesis of dna and protein was ... | 1988 | 2461791 |
| expression of cardiac sarcolemmal na+-ca2+ exchange activity in xenopus laevis oocytes. | injection of xenopus laevis oocytes with rabbit heart poly(a)+rna results in expression of na+ inside (nai+)-dependent ca2+ uptake activity. the activity was measured by first loading the oocytes with na+ using nystatin and then incubating the oocytes in k+ or na+ medium containing 45ca. the expressed na+ gradient-dependent ca2+ uptake was five to eight times that observed with water-injected oocytes or with poly(a)+rna-injected oocytes for which the na+ load step had been omitted. induced activ ... | 1988 | 2462361 |
| xenopus endo b is a keratin preferentially expressed in the embryonic notochord. | screening of a cdna library from neurula stage xenopus laevis for notochord-specific sequences led to the isolation of a cdna clone, xk endo b (xenopus keratin endo b), which encodes a nonepidermal type i keratin. in situ and northern blot hybridizations indicate that expression of xk endo b rna is concentrated in the notochord, whereas expression in the endoderm is 5-10 times lower. xk endo b mrna is present in the oocyte and increases from late gastrula. accumulation peaks by late neurula and ... | 1988 | 2463213 |
| identities, antigenic determinants, and topographic distributions of neurofilament proteins in the nervous systems of adult frogs and tadpoles of xenopus laevis. | three proteins with nominal molecular weights of 73 kda (xnf-l), 175 kda (xnf-m), and 205 kda (xnf-h) were identified as putative neurofilament proteins in the nervous system of the frog, xenopus laevis. these conclusions were based on four criteria: (1) these proteins were enriched in cytoskeletal preparations; (2) they reacted with a monoclonal antibody (anti-ifa) that cross-reacts with an epitope found in all intermediate filament proteins; (3) they cross-reacted with monoclonal antibodies di ... | 1988 | 2463277 |
| ultrastructural study of contacts between cells of the dorsal ectoderm and chordamesoderm during gastrulation in xenopus laevis. | in gastrulae of xenopus laevis, various morphological types of intercellular approximation occur between the dorsal ectoderm and chordamesoderm. ruthenium red staining reveals that in some areas the glycocalyces of heterotypic cells appear to come into contact. these observations, in conjunction with the results of previous studies, suggest that cell contacts offer a possible pathway for the transmission of inductive stimuli, and that they may be important in the regionalization of the neuralize ... | 1988 | 2463727 |
| mediolateral cell intercalation in the dorsal, axial mesoderm of xenopus laevis. | the pattern of mediolateral cell intercalation in mesodermal tissues during gastrulation and neurulation of xenopus laevis was determined by tracing cells labeled with fluorescein dextran amine (fda). patches of the involuting marginal zone (imz) of early gastrula stage embryos, labeled by injection of fda at the one-cell stage, were grafted to the corresponding regions of unlabeled host embryos. the host embryos were fixed at several stages, serially sectioned, and examined with fluorescence mi ... | 1989 | 2463948 |
| xenopus spermatozoon: is there any correlation between motility and oxygen consumption? | the motility status of xenopus laevis spermatozoa does not affect their respiration rate. oxygen consumption for 10(9) spermatozoa is approximately 0.4 mumol/minute. oxygen consumption is not increased by gramicidin d, an uncoupler, and it is not blocked by kcn or nan3. the adenosine triphosphate (atp) content of spermatozoa that have been activated is definitely less than that in the spermatozoa that remained immotile. incubation in kcn, nan3, and gramicidin decreases the atp content and impair ... | 1988 | 2464532 |
| expression of type i iodothyronine 5'-deiodinase in xenopus laevis oocytes. | the enzymes mediating the conversion of thyroxine to 3,5,3'-triiodothyronine have proved difficult to purify and characterize biochemically. in this report we describe the successful expression in xenopus laevis oocytes of type i iodothyronine 5'-deiodinase. oocytes injected with rat liver mrna and then incubated for 5 days demonstrated a progressive increase in 5'-deiodinase activity. this activity: (a) manifested a km for 3,3',5'-triiodothyronine of 0.24 microm, (b) was sensitive to inhibition ... | 1989 | 2464594 |
| the genes for the frog skin peptides gla, xenopsin, levitide and caerulein contain a homologous export exon encoding a signal sequence and part of an amphiphilic peptide. | from genomic libraries of xenopus laevis, parts of the genes coding for the precursors of the skin peptides gla (peptide with amino-terminal glycine and carboxy-terminal leucinamide), xenopsin and levitide have been isolated and sequenced. the gene for prepropeptide gla comprises four exons, separated by relatively small introns. the gene for preproxenopsin is composed of five exons, of which all but the last one have been analyzed. this is a large gene encompassing at least 25,000 base pairs. i ... | 1989 | 2465151 |
| effect of magnetic resonance imaging on xenopus laevis embryogenesis. | xenopus laevis embryos, exposed to various lengths of magnetic resonance imaging (mri), demonstrated no abnormal morphology, function, or developmental delays. the overall protein profiles and nucleic acid ratios were similar compared to controls. results suggest there are no adverse effects of mri components on the development of this vertebrate. | 1988 | 2465471 |
| translation in xenopus laevis oocytes of hybrid selected lew rat rt1.b alpha- and beta-chain transcripts results in serologically discrete class ii polypeptide chain complexes. | using the non-crossreactive mab mrc-ox3 and mrc-ox6, two serologically distinct rt1.b-specific (i-a equivalent) alpha, beta heterodimers have previously been described by us as residing at the cell surface of lew rat spleen cells. the two-chain elements were suggested to represent stable conformation isomers, diverged by dissociation of the mature gamma-chain from a mab mrc-ox6 reactive biosynthetic intermediate, composed of terminally glycosylated alpha-, beta- and gamma-chains. in this study w ... | 1989 | 2465490 |
| [behavior of exogenously introduced dnas and expression of their genetic information in developing embryos of xenopus laevis]. | | 1988 | 2465559 |
| loss of material from the retrograde axonal transport system in frog sciatic nerve. | rapid axonal transport was studied in sciatic nerve preparations of the amphibian xenopus laevis maintained in vitro at 23.0 +/- 0.2 degrees c. a pulse of [35s]methionine-labeled material was allowed to move in the anterograde direction until encountering a lesion, at which a portion of the pulse reversed directions and moved in the retrograde direction. by constricting the nerve during the course of the experiment, it was possible to prevent continuous return of label from the lesion, thus crea ... | 1989 | 2466951 |
| structure and expression of a xenopus gene encoding an snrnp protein (u1 70k). | a cdna and two genes for the xenopus laevis u snrnp 70k protein have been cloned and partially sequenced. the cdna encodes a protein whose predicted mol. wt is 57 kd but which migrates as a 70 kd protein in sds-page when translated in vitro from a cdna transcript. the predicted protein sequences of the human and xenopus u1 70k are shown to be very similar. analysis of several genomic clones suggests that there are at least two, and possibly more, different genes coding for the 70k protein in the ... | 1988 | 2468488 |
| changes in the polyadenylation of specific stable rna during the early development of xenopus laevis. | the distribution of four specific rna species between the poly(a)+ and poly(a)- fractions has been studied during the first hours of xenopus laevis development, before the mid-blastula transition (mbt). two of these specific rna species correspond to clones selected by differential hybridization from a xenopus egg cdna library. another corresponds to xenopus c-raf mrna and the last one to rna revealed by a mouse ornithine decarboxylase probe. we show that two of these rnas are adenylated after f ... | 1988 | 2468559 |
| weak bases mimic the fertilization-associated chloride conductance increase and induce morphological changes in the cortex of xenopus laevis eggs. | ammonia and other weak bases (methylamine, trimethylamine) including certain local anesthetics (benzocaine, procaine, lidocaine) depolarized the plasma membrane of unactivated xenopus eggs. exposure to different [cl-]o or to the other halides (f-, br-, i-) revealed a similar anion dependency of the weak base-induced conductance change to that found for the normal fertilization potential. although transient, the induced depolarization was slower and of longer duration than the fertilization poten ... | 1989 | 2469526 |
| high initiation rates at the ribosomal gene promoter do not depend upon spacer transcription. | we report experiments that test the model that in xenopus laevis, rna polymerase i is "handed over" in a conservative fashion from the t3 terminator to the adjacent gene promoter. we have introduced transcription-terminating lesions into the ribosomal dna repeat by irradiating cultured cells with ultraviolet light. we used isolated nuclei to measure the effect of such lesions on transcription. uv damage sufficient to prevent all elongating rna polymerase from reaching t3 from upstream had no adv ... | 1989 | 2470092 |
| a major single-stranded dna binding protein from ovaries of the frog, xenopus laevis, is lactate dehydrogenase. | the most abundant single-stranded dna binding protein (ssb) found in ovaries of the frog, xenopus laevis, was purified to electrophoretic homogeneity. under physiological conditions, the purified ssb lowered the tm of poly[d(a-t)] and stimulated dna synthesis by the homologous dna polymerase dna primase alpha complex on single-stranded dna templates. these properties are characteristic of a bona fide single-stranded dna binding protein. the stokes radius of native ssb was calculated to be 45 a, ... | 1989 | 2470407 |
| 5 alpha-dihydrotestosterone has nonspecific effects on membrane channels and possible genomic effects on ach-activated channels. | 1. myotubes cultured from adult male xenopus laevis laryngeal muscle have been found to express androgen receptors. 2. using patch-clamp techniques, it was found that 5 alpha-dihydrotestosterone (5 alpha-dht) can act directly at membranes of these myotubes to alter the kinetic properties of acetylcholine- (ach) activated single channels. 3. when the culture medium contains 5 alpha-dht for greater than 6 days, the androgen acts through its receptors to markedly increase ach-activated, single-chan ... | 1989 | 2470867 |