| plasmid and bacteriophage lambda-dna show differential replication characteristics following injection into fertilized eggs of xenopus laevis: dependence on period and site of injection. | the fate of dna injected into in vitro fertilized eggs of xenopus laevis during subsequent early embryogenesis was investigated by changing the time period and the area of injection. form i/ii plasmid dna was found to be preferentially replicated in embryos which had been injected 60-65 min after fertilization into the animal half of the fertilized egg, irrespective of the presence of a eukaryotic origin of replication sequence element in the dna probe used for injection. in the experiments wher ... | 1990 | 2140953 |
| selective carboxyl methylation of structurally altered calmodulins in xenopus oocytes. | the eucaryotic protein carboxyl methyltransferase specifically modifies atypical d-aspartyl and l-isoaspartyl residues which are generated spontaneously as proteins age. the selectivity of the enzyme for altered proteins in intact cells was explored by co-injecting xenopus laevis oocytes with s-adenosyl-l-[methyl-3h]methionine and structurally altered calmodulins generated during a 14-day preincubation in vitro. control experiments indicated that the oocyte protein carboxyl methyltransferase was ... | 1990 | 2123492 |
| the degradation sequence of adenovirus e1a consists of the amino-terminal tetrapeptide met-arg-his-ile. | the adenovirus e1a gene product is a potent transcriptional activator and nuclear oncoprotein. like other regulatory proteins, e1a has a short half-life, in the range of 30 to 120 min. this short half-life, which was measured in cells synthesizing e1a, is not observed in cells injected with e1a protein made in bacteria or in vitro. in these cases, e1a is essentially refractory to degradation. in an attempt to reconcile this apparent paradox, we suggested that e1a was marked for degradation durin ... | 1990 | 2146491 |
| vitellogenesis in xenopus laevis and chicken: cognate ligands and oocyte receptors. the binding site for vitellogenin is located on lipovitellin i. | vitellogenesis is the process of yolk formation in rapidly growing oocytes of oviparous species. the transport of yolk precursor proteins from the blood plasma into the oocyte is achieved by receptor-mediated endocytosis. although the xenopus oocyte is one of the prime experimental systems for expression of foreign genes and their products, the receptor for the main vitellogenic protein, vitellogenin, from this extensively utilized cell has not been identified. here we have applied ligand and im ... | 1990 | 2153117 |
| downregulation of surface sodium pumps by endocytosis during meiotic maturation of xenopus laevis oocytes. | during meiotic maturation, plasma membranes of xenopus laevis oocytes completely lose the capacity to transport na and k and to bind ouabain. to explore whether the downregulation might be due to an internalization of the sodium pump molecules, the intracellular binding of ouabain was determined. selective permeabilization of the plasma membrane of mature oocytes (eggs) by digitonin almost failed to disclose ouabain binding sites. however, when the eggs were additionally treated with 0.02% sodiu ... | 1990 | 2154110 |
| expression of biologically active human platelet-derived growth factor (pdgf) b-receptor in xenopus laevis oocytes. | platelet-derived growth factor (pdgf) consists of three different isoforms, pdgf-aa, pdgf-ab and pdgf-bb, which bind to at least two types of receptors: the b-receptor, to which only pdgf-bb binds, and the a/b receptor, to which all three isoforms bind. microinjection of synthetic mrna in xenopus laevis oocytes was used to obtain cell-surface expression of the human pdgf b-receptor. the production of receptor molecules of correct size (190 kd) was demonstrated by specific immunoprecipitation; th ... | 1990 | 2154197 |
| formation of inositol pentakisphosphate by ovarian follicles of xenopus laevis from metabolism of inositol (1,4,5)trisphosphate and inositol (1,3,4,5)tetrakisphosphate and from receptor activation. | small amounts of a higher inositol phosphate with chromatographic properties of [3h]inositol (1,3,4,5,6)pentakisphosphate were formed from [3h]inositol (1,4,5)trisphosphate added to homogenates of ovarian follicles of xenopus laevis, and from [3h]inositol (1,3,4,5)tetrakisphosphate after injection into follicular oocytes. other intermediate forms of inositol tetrakisphosphate were not detectable. [3h]inositol (1,3,4,5,6)pentakisphosphate prepared from chicken erythrocytes was metabolized in homo ... | 1990 | 2154206 |
| nucleotide sequence determination of mouse, chicken and xenopus laevis rig cdnas: the rig-encoded protein is extremely conserved during vertebrate evolution. | mouse, chicken and xenopus laevis homologues to rig (rat insulinoma gene) cdna were isolated and their nucleotide sequences were determined. each homologue encoded a 145-amino acid protein; the amino acid sequence remained invariant in the murine and avian genes, and there were only 6 amino acid substitutions in the salientian gene. the evolutionary rate calculated for rig mrna was sufficiently low to be viewed as evidence that rig is vital to vertebrate species. southern blot analysis indicated ... | 1990 | 2154983 |
| absence of substantial bending in xenopus laevis transcription factor iiia-dna complexes. | the extent and location of dna-bending induced in the xenopus laevis transcription factor iiia-oocyte 5s rna gene complex was determined by the gel retardation method. the electrophoretic mobilities of tfiiia complexed with restriction fragments of 160, 177, 282 and 300 bp that contain the sequence of the major oocyte 5s rna gene were compared. in these fragments the 120-bp gene is positioned either in the middle or at the end. minor differences in the mobility of the complexes indicate that the ... | 1990 | 2155404 |
| functional reconstitution of fmet-leu-phe receptor in xenopus laevis oocytes. | fmet-leu-phe (fmlp) receptors were functionally reconstituted into xenopus laevis oocytes by microinjection with rna isolated from promyelocytic leukemia cells (hl-60) differentiated with 750 microm n6, o2-dibutyryl cyclic adenosine 3',5'-monophosphate. fmlp-induced ca2+ mobilization was monitored by measurement of photon emission elicited by aequorin coinjected with rna into albino x. laevis oocytes. maximal expression of the fmlp receptor was achieved 48 h after microinjection of rna. dose-res ... | 1990 | 2156834 |
| calcium wave evoked by activation of endogenous or exogenously expressed receptors in xenopus oocytes. | the mrna encoding the cloned substance k receptor was microinjected into xenopus laevis oocytes. after expression of the mrna, ca2+ was imaged in the oocytes with a digital imaging fluorescence microscopy system using the ca2(+)-sensitive dyes fura-2 and fluo-3. application of substance k caused a dose-related wave of ca2+ mobilization to spread from a focus and to elevate the ca2+ concentration in the oocyte. activation of endogenous muscarinic or angiotensin ii receptors in noninjected oocytes ... | 1990 | 2157216 |
| orthopoxvirus gene expression in xenopus laevis oocytes: a component of the virion is needed for late gene expression. | we have examined the feasibility of using xenopus laevis oocytes microinjected with rabbit poxvirus as a system to study poxvirus gene expression. the injection of either intact virus or subviral cores resulted in accurate synthesis of viral proteins. this expression was dependent on the multiplicity of injected virus, with the optimal injected dose being equivalent to approximately 300 pfu per oocyte. extensive viral gene expression including late viral protein synthesis was observed when intac ... | 1990 | 2157885 |
| characterization of a na(+)-k(+)-2cl- cotransport system in oocytes from xenopus laevis. | in order to characterize the transport systems mediating k+ uptake into oocytes, flux studies employing 86rb were performed on xenopus oocytes stripped of follicular cells by pretreatment with ca2(+)-mg2(+)-free barth's medium. total rb+ uptake consisted of an ouabain-sensitive and an ouabain-insensitive flux. in the presence of 100 mmol/l nacl and 0.1 mmol/l ouabain the ouabain-insensitive flux amounted to 754.7 +/- 59.9 pmol/oocyte per h (n = 30 cells, i.e., 10 cells each from three different ... | 1990 | 2158348 |
| oxytocin receptors from llc-pk1 cells: expression in xenopus oocytes. | two selective radioligands for oxytocin receptors, [3h]-[4-threonine,7-glycine]oxytocin [( 3h]-[thr4,gly7]ot) and 125i-[1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid), 2-(o-methyl)tyrosine, 4-threonine, 8-ornithine, 9-tyrosine amide]-oxytocin (125i-ota), were used to characterize oxytocin receptors from two pig kidney-derived cell lines, llc-pk1 and llc-pk1l. [3h]-[thr4,gly7]ot and 125i-ota bind with high affinity (mean kd values of 14 and 0.06 nm, respectively) to the same popula ... | 1990 | 2158746 |
| postnatal development of voltage-dependent calcium channels in the mouse brain disclosed by the xenopus oocyte assay. | we assessed the ontogeny of murine voltage-dependent calcium channels by extracting mrna from brains of mice at different postnatal ages and injecting the mrna into oocytes of the frog, xenopus laevis. voltage-dependent ca2(+)-activated cl- channels were measured to assess the presence of ca2(+) channels. when compared with water-injected oocytes (controls), an increase in ca2(+) channels was not detected until postnatal day 7. the number of ca2+ channels peaked between 9 and 18 days and began t ... | 1990 | 2159399 |
| functional expression of ca2(+)-mobilizing alpha-thrombin receptors in mrna-injected xenopus oocytes. | alpha-thrombin (th) initiates a program of intracellular events that lead to dna replication in quiescent ccl39 chinese hamster lung fibroblasts via membrane receptors that have yet to be characterized at a molecular level. functional th receptors were expressed in xenopus laevis oocytes following injection of poly(a)+ rna from th-responsive ccl39 cells; their presence was demonstrated by th-stimulated 45ca2+ efflux or ca2(+)-dependent cl- channel activation. in voltage clamp experiments on micr ... | 1990 | 2159419 |
| isolation and characterization of a tyrosyl phosphatase activator from rabbit skeletal muscle and xenopus laevis oocytes. | ptpa, a specific phosphotyrosyl phosphatase activator of the pcsh2 and pcsl protein phosphatases, was purified up to apparent homogeneity from xenopus laevis ovaries and rabbit skeletal muscle and highly purified from dog liver. ptpa appears as a 40-kda protein in gel filtration, as well as in sucrose gradient centrifugation, and as a 37-39-kda protein doublet in sds-page. its estimated cellular concentration of 0.75 microm in oocytes or 0.25 microm in rabbit skeletal muscle is suggestive of an ... | 1990 | 2159785 |
| metabolism of the biologically active inositol phosphates ins(1,4,5)p3 and ins(1,3,4,5)p4 by ovarian follicles of xenopus laevis. | the metabolism of biologically active inositol phosphates in developed ovarian follicles from xenopus laevis was investigated. techniques used were microinjection of tracer into the intact oocyte coupled by gap junctions to follicle cells, as well as addition of tracer to homogenates of ovarian follicles and to homogenates of oocytes stripped of outer follicle-cell layers. metabolism was similar to that previously described for other types of cell and tissue, with several unusual features. homog ... | 1990 | 2160808 |
| molecular biology of mammalian amino acid receptors. | the amino acid receptor proteins are ubiquitous transducers of most excitatory and inhibitory synaptic transmission in the brain. in july 1987 two reports appeared describing the molecular cloning of a pair of subunits of the gabaa receptor (7) and one subunit of the glycine receptor (13). these papers sparked wide interest and led quickly to the concept of a ligand-gated receptor-ion channel superfamily that includes nicotinic acetylcholine receptors as well as certain amino acid receptors. the ... | 1990 | 2161372 |
| regulation of na+ channels in frog lung epithelium: a target tissue for aldosterone action. | sodium transport across isolated lung tissue of the frog xenopus laevis was measured in ussing chambers under voltage-clamp conditions. perfusing the lungs with nacl-ringer's solutions on both sides, a basal distinct amiloride-blockable na+ current was present. incubating the lungs with 1 mumol/l aldosterone from the pleural side raised the short circuit current after a 1-h latent period. maximal values were reached after 4-5 h of aldosterone treatment, at which time the transepithelial na+ curr ... | 1990 | 2162035 |
| morphology of the pars intermedia and the melanophore-stimulating cells in xenopus laevis in relation to background adaptation. | the melanophore-stimulating hormone (msh) cells of the amphibian pars intermedia secrete the peptide alpha-melanophore-stimulating hormone (alpha-msh), which induces pigment dispersion in dermal melanophores. the purpose of the present study was to determine (1) whether prolonged activation of the secretory activity of the pars intermedia is associated with hypertrophy, hyperplasia, or both and (2) whether the msh cells function as a homogeneous or heterogeneous population in meeting the physiol ... | 1990 | 2162308 |
| functional expression of b2 bradykinin receptors from balb/c cell mrna in xenopus oocytes. | the murine balb/c 3t3 fibroblast clone sv-t2 (3t3 cells) expresses receptors for the nonapeptide bradykinin. in these cells, bradykinin stimulates both inositol phosphate (insp) formation and arachidonic acid release by independently activating phospholipase c and phospholipase a2, respectively. these actions of bradykinin are mediated by a receptor(s) coupled to pertussis toxin-insensitive guanine nucleotide-binding proteins. bradykinin-stimulated increases in insp lead to the mobilization of i ... | 1990 | 2163013 |
| characterization of a maternal type vi collagen in xenopus embryos suggests a role for collagen in gastrulation. | we characterized a novel extracellular matrix element that is present in the earliest developmental stages of xenopus laevis, and is recognized by an mab 3d7. based on amino acid composition, breakdown patterns by bacterial collagenases, and the molecular weights of the components of the antigen (240, 200, and 140 kd), we found it very similar to mammalian collagen type vi. the antigen is evenly distributed in unfertilized eggs. shortly after fertilization, it becomes localized intracellularly i ... | 1990 | 2164030 |
| action of light on frog pigment cells in culture. | solar radiation induces numerous biologic effects in skin but the mechanism underlying these responses is poorly understood. to study the etiology of these phenomena, we investigated the effect of light on cultured xenopus laevis melanophores. visible light stimulated a marked increase in intracellular camp levels within the first minute of irradiation. this light-induced elevation in camp was blocked by melatonin and was not seen in fibroblasts irradiated in a similar manner. these data show th ... | 1990 | 2165596 |
| restoration of the plasticity of binocular maps by nmda after the critical period in xenopus. | visual input during a critical period of development plays a major role in the establishment of orderly connections in the developing visual system. in xenopus laevis, the matching of visual maps from the two eyes to the optic tectum depends on binocular visual input during the critical period, which extends from late tadpole to early juvenile stages. alterations in eye position, which produce a mismatch of the tectal maps, normally evoke a compensatory adjustment in the map of the ipsilateral e ... | 1990 | 2166343 |
| regulation of oogenesis: the piscine receptor for vitellogenin. | the receptor-mediated uptake of vitellogenin (vtg), a plasmatic lipophosphoglycoprotein, is crucial for oocyte growth in egg-laying animals. the plasma membrane receptor for vtg was characterized from oocytes of coho salmon, oncorhynchus kisutch. in direct binding studies, the receptor exhibited high affinity (kd, 180 nm) for salmonid vtg, and by ligand blotting with radiolabelled vtg it was visualized as a protein with an apparent mr of 100,000, under non-reducing conditions. the fish vtg recep ... | 1990 | 2167133 |
| micromolar free calcium exposes ouabain-binding sites in digitonin-permeabilized xenopus laevis oocytes. | as demonstrated previously, digitonin-permeabilized xenopus oocytes have a large internal pool of sodium pumps which are inaccessible to cytosolic ouabain [schmalzing, kröner & passow (1989) biochem. j. 260, 395-399]. access to internal ouabain-binding sites required permeabilization of inner membranes with sds. in the present study, micromolar free ca2+ was found to stimulate ouabain binding in the digitonin-permeabilized cells (k0.5 0.5 microm-ca2+, h 1.9, average of seven experiments) without ... | 1990 | 2167664 |
| ca-sensitive sodium absorption in the colon of xenopus laevis. | transepithelial electrogenic na transport (ina) was investigated in the colon of the frog xenopus laevis with electrophysiological methods in vitro. the short circuit current (isc) of the voltage-clamped tissue was 24.2 +/- 1.8 microa.cm-2 (n = 10). about 60% of this current was generated by electrogenic na transport. removal of ca2+ from the mucosal ringer solution stimulated ina by about 120%. ina was not blockable by amiloride (0.1 mmol.l-1), a specific na-channel blocker in epithelia, but a ... | 1990 | 2167905 |
| sn-1,2-diacylglycerol levels increase in progesterone-stimulated xenopus laevis oocytes. | full-grown xenopus laevis oocytes resume meiosis from prophase arrest in response to progesterone stimulation. recent studies have shown that the tumor promoter, 12-o-tetradecanoylphorbol 13-acetate (tpa), a very potent activator of protein kinase c, can also induce the resumption of meiosis in amphibian oocytes. we have investigated the possibility that sn-1,2-diacylglycerol (dag), the intracellular activator of protein kinase c, may be involved in the pathway normally used by progesterone. we ... | 1990 | 2167919 |
| activation of two different receptors mobilizes calcium from distinct stores in xenopus oocytes. | acetylcholine (ach) and thyrotropin-releasing hormone (trh) utilize inositol 1,4,5-trisphosphate (ip3) as a second messenger and evoke independent depolarizing membrane electrical responses accompanied by characteristic 45ca efflux profiles in xenopus laevis oocytes injected with gh3 pituitary cell mrna. to determine whether this could be accounted for by mobilization of calcium from functionally separate stores, we measured simultaneously 45ca efflux and membrane electrical responses to ach and ... | 1990 | 2168222 |
| a possible role of the beta-subunit of (na,k)-atpase in facilitating correct assembly of the alpha-subunit into the membrane. | mrnas from the alpha- and beta-subunits (mrna alpha and mrna beta, respectively) of torpedo californica (na,k)-atpase were injected into xenopus laevis oocytes either separately or in combination, and the properties of the two subunits synthesized were studied. the alpha-subunit synthesized in oocytes injected with mrna alpha alone was recovered in both the membrane and cytosol fractions and was susceptible to tryptic attack. when mrna beta was coinjected with mrna alpha, almost all the alpha-su ... | 1990 | 2168428 |
| microinjected gtp-gamma-s inhibits progesterone-induced maturation of xenopus oocytes. | gtp-gamma-s inhibits progesterone-induced maturation of xenopus laevis oocytes and induces a rise in their camp levels. gtp-gamma-s does not inhibit mpf-induced maturation. although gtp-gamma-s prevents the progesterone-induced increases in protein synthesis and phosphorylation, it has no effect on the basal rates of either. gtp-gamma-s also prevents the initial dag drop induced by progesterone. gdp-beta-s effects are ambiguous, but it seems not to affect progesterone-induced maturation. these r ... | 1990 | 2170213 |
| expression of epithelial na channels in xenopus oocytes. | epithelial na channel activity was expressed in oocytes from xenopus laevis after injection of mrna from a6 cells, derived from xenopus kidney. poly a(+) rna was extracted from confluent cell monolayers grown on either plastic or permeable supports. 1-50 ng rna was injected into stage 5-6 oocytes. na channel activity was assayed as amiloride-sensitive current (ina) under voltage-clamp conditions 1-3 d after injection. ina was not detectable in noninjected or water-injected oocytes. this amilorid ... | 1990 | 2170563 |
| expression of neurotrophic activity in xenopus oocytes injected with mrna from wounded rat cerebral cortex. | injury to the cerebral cortex of the rat brain has been shown to induce the expression of neurotrophic factors for dissociated peripheral and central neurons in culture. we confirm this phenomenon and report that xenopus laevis oocytes injected with mrna extracted from wounded rat cortex expressed similar neurotrophic activity. to detect the low amounts of neurotrophic factors that could be expected from the oocyte translation system, a miniaturization of the assay for neurotrophic and cell-surv ... | 1990 | 2170801 |
| localization of endogenous galactoside-binding lectin during morphogenesis of xenopus laevis. | a monoclonal antibody has been produced against xenopus laevis galactoside-binding neural-crest-stage lectin. this antibody inhibits lectin-mediated hemagglutination. using this antibody in conjunction with immunohistochemical techniques, lectin deposition has been studied in embryos and tadpoles at different stages of morphogenesis, from initial neural crest migration, up to the formation of a swimming tadpole. lectin levels change during development in different regions of the embryo and tadpo ... | 1990 | 2123609 |
| potential for two isoforms of the a1 ribonucleoprotein in xenopus laevis. | we have identified the xenopus cognates for the rna-binding protein a1. this protein has previously been shown to be one of the components of the heterogeneous nuclear ribonucleoprotein (hnrnp) complex in rat and human cells. we have isolated several xenopus clones from oocyte, tailbud embryo, and leg muscle cdna libraries and determined their nucleotide sequences. potentially, two different a1 isoforms are expressed in xenopus; they have been termed xa1a and xa1b. besides insertions and deletio ... | 1990 | 2137612 |
| development and innervation of the abdominal muscle in embryonic xenopus laevis. | the morphogenesis and innervation of the ventral abdominal musculature in xenopus embryos was examined using microscopic techniques. muscle development begins at nieuwkoop and faber stage 31, when aggregates of undifferentiated cells form on the ventrolateral margins of rostral trunk myotomes. during subsequent stages, aggregates form and detach from progressively more caudal myotomes to form a series of seven discrete cell clusters (anlagen). the anlagen migrate ventrally in a cell-free space b ... | 1990 | 2141230 |
| assembly of correctly spaced chromatin in a nuclear extract from xenopus laevis oocytes. | assembly of nucleosomes on relaxed, covalently closed dna has been studied in a nuclear extract of xenopus laevis oocytes. nucleosomes containing the four histones h3, h4, h2a and h2b but lacking histone h1 are readily assembled on the dna. the pattern of micrococcal nuclease digestion shows that the nucleosomes assembled in the absence of atp and mg (ii) are closely packed, with a periodicity of 150 base pairs (bp). in contrast, in the presence of atp and mg (ii) the spacing of the nucleosomes ... | 1990 | 2170936 |
| contribution of ventral blood island mesoderm to hematopoiesis in postmetamorphic and metamorphosis-inhibited xenopus laevis. | in an effort to label very early erythrocyte and lymphocyte populations and to follow their fate in normally developing postmetamorphic frogs and goitrogen-treated permanent larvae, diploid (2n) and triploid (3n) ventral blood island (vbi) mesoderm was exchanged between neurula stage embryos (about 16-22 hr old). beginning at 15 days of age, half of the 2n or 3n hosts were treated with sodium perchlorate to prevent thyroxine-induced developmental changes. at larval stages 55-59 (41-48 days) and ... | 1990 | 2172056 |
| glycinergic contacts in the outer plexiform layer of the xenopus laevis retina characterized by antibodies to glycine, gaba and glycine receptors. | electrophysiological experiments have predicted a direct synaptic input from glycinergic interplexiform cells (ipcs) to gabaergic horizontal cells in the xenopus retina. however, previous ultrastructural studies failed to demonstrate this input. here, we used three immunocytochemical approaches to investigate this issue. first, double-label postembedding immunocytochemistry with gaba- and glycine-like immunoreactivity (gaba-li and glycine-li) was used to study possible interactions of the glycin ... | 1990 | 2172330 |
| detection of n-acetylated forms of beta-endorphin and nonacetylated alpha-msh in the intermediate pituitary of the toad, bufo marinus. | steady-state analysis of the acid extracts of the intermediate pituitary of the toad, bufo marinus, revealed the presence of multiple forms of beta-endorphin and alpha-msh. approximately 98% of the immunoreactive beta-endorphin was n-acetylated. the major form of n-acetylated beta-endorphin, which represented 81.5% of the total beta-endorphin recovered from this tissue, had an apparent molecular weight of 1.2 kda and a net charge of +1 at ph 2.75. approximately 98% of the immunoreactive alpha-ms ... | 1990 | 2172945 |
| cdna cloning and expression in xenopus laevis oocytes of pig renal dipeptidase, a glycosyl-phosphatidylinositol-anchored ectoenzyme. | clones expressing renal dipeptidase (ec 3.4.13.11) have been isolated from a pig kidney cortex cdna library after employing the polymerase chain reaction technique to amplify a region of the dipeptidase cdna. the complete primary sequence of the enzyme has been deduced from a full length cdna clone. this predicts a protein of 409 amino acids, a cleavable n-terminal signal sequence of 16 residues and two n-linked glycosylation sites. at the c-terminus of the predicted sequence is a stretch of mai ... | 1990 | 2173907 |
| a protein factor from xenopus oocytes with simian virus 40 large tumor antigen-like dna supercoiling activity. | the atp-dependent movement of simian virus 40 large tumor antigen on dna can cause positive supercoiling of template dna in the presence of bacterial dna topoisomerase i, which specifically relaxes negative supercoils. with such a supercoiling assay, an activity capable of atp-dependent, positive supercoiling of dna in the presence of bacterial dna topoisomerase i was found in 7s particles prepared from xenopus laevis oocytes but not in purified transcription factor iiia. the positive supercoils ... | 1990 | 2174551 |
| a nervous system-specific isotype of the beta subunit of na+,k(+)-atpase expressed during early development of xenopus laevis. | we have previously described the isolation of several genes expressed exclusively in the nervous system of adult xenopus laevis and activated in the embryo shortly after neural induction. the sequence of one of these cdnas, 24-15, identifies the corresponding protein as an isotype of the beta subunit of na+,k(+)-atpase [atp phosphohydrolase (na+/k(+)-transporting); ec 3.6.1.37]. this form is distinct from the previously described beta 1 subunit of xenopus, and the protein sequence comparison sug ... | 1990 | 2174552 |
| isolation, localization, and cloning of a kainic acid binding protein from frog brain. | excitatory amino acids (eaa) are major neurotransmitters in the vertebrate central nervous system. eaa receptors have been divided into three major subtypes on the basis of electrophysiological and ligand binding studies: n-methyl-d-aspartate, kainate, and quisqualate receptors. to understand their molecular properties, we undertook a project aimed at isolation and cloning of these receptor subtypes. we purified a kainate binding protein (kbp) from frog brain, in which kainate binding sites are ... | 1990 | 2174936 |
| expression cloning of a cdna encoding the mouse pituitary thyrotropin-releasing hormone receptor. | thyrotropin-releasing hormone (trh) is an important extracellular regulatory molecule that functions as a releasing factor in the anterior pituitary gland and as a neurotransmitter/neuromodulator in the central and peripheral nervous systems. binding sites for trh are present in these tissues, but the trh receptor (trh-r) has not been purified from any source. using xenopus laevis oocytes in an expression cloning strategy, we have isolated a cdna clone that encodes the mouse pituitary trh-r. thi ... | 1990 | 2175902 |
| identification and functional expression of a novel ligand binding subunit of the inhibitory glycine receptor. | by homology screening of a rat brain cdna library we have identified a novel alpha subunit variant of the inhibitory glycine receptor, alpha 3. the deduced protein exhibits 82-83% amino acid identity to the previously characterized rat and human alpha 1 and alpha 2 subunit sequences. upon heterologous expression in xenopus laevis oocytes, the alpha 3 subunit formed functional agonist-gated chloride channels which displayed a low affinity for glycine and only small responses to taurine. amplifica ... | 1990 | 2176214 |
| activation of protein kinase c by phorbol ester induces downregulation of the na+/k(+)-atpase in oocytes of xenopus laevis. | full-grown prophase-arrested oocytes of xenopus laevis were treated with 50 nm phorbol 12-myristate 13-acetate (pma), an activator of protein kinase c, or with 50 nm 4 alpha-phorbol 12,13-didecanoate (4 alpha pdd) that does not activate protein kinase c. the effect on membrane currents and capacitance, inulin uptake and ouabain binding, and on membrane morphology were analyzed. (i) during application of pma, current generated by the na+/k+ pump decreases; in addition, cl- and k+ channels become ... | 1990 | 2176238 |
| nucleoside diphosphate kinase from xenopus oocytes; partial purification and characterization. | we have identified and partially purified a soluble nucleoside diphosphate kinase (ndp kinase) from xenopus laevis oocytes. the enzyme preparation can catalyze the transfer of phosphate from atp to all of the major oxy- and deoxynucleotides. it can also catalyze the transfer of a phosphorothioate group from gamma-s-atp to an acceptor gdp forming gamma-s-gtp. like ndp kinases from other sources, the catalytic mechanism appears to involve a phosphoenzyme intermediate which can be isolated. transfe ... | 1990 | 2176546 |
| amino acid receptors from insect muscle: electrophysiological characterization in xenopus oocytes following expression by injection of mrna. | poly(a)+ messenger ribonucleic acid (mrna) was extracted from leg muscles of the locust schistocerca gregaria and injected into oocytes of xenopus laevis. after 5-10 days incubation, receptors for l-glutamate, l-quisqualate, dl-ibotenate and gamma-aminobutyric acid (gaba) were expressed. agonist-induced currents were dose-dependent, and, in the concentration range 1 microm to 1 mm, generally had peak values of 50 na. the responses to all agonists, apart from gaba, exhibited desensitization which ... | 1990 | 2176711 |
| different-sized mrnas from gh4c1 cells induce a trh-dependent electrical response in xenopus laevis oocytes. | poly(a)+ rna from the gh4c1 rat pituitary cell line elicited a thyrotropin releasing hormone response in xenopus laevis oocytes which could be measured as a change in membrane current by the voltage-clamp method. oocytes injected with poly(a)+ rna from gh12c1 cells which do not bind thyrotropin releasing hormone or with buffer solution alone did not show this response. size fractionation of total poly(a)+ rna by sucrose density-gradient centrifugation shows two response maximal representing vari ... | 1990 | 2177312 |
| distribution of integrins and their ligands in the trunk of xenopus laevis during neural crest cell migration. | we have examined the distribution in xenopus embryos of beta 1 subunits of integrin, as recognized by cross-reactive antibodies against the avian integrin beta 1 subunit. these antibodies recognize a doublet of bands of approximately 120 kd in xenopus embryos. the distribution pattern of these integrin cell surface receptors was compared with that of two possible ligands, fibronectin and laminin, in the extracellular matrix during the time of neural crest cell migration. integrin immunoreactivit ... | 1990 | 2179461 |
| structural analysis of the internal transcribed spacer 2 of the precursor ribosomal rna from saccharomyces cerevisiae. | full-length precursor ribosomal rna molecules (6440 bases) were produced in vitro using a plasmid containing the yeast 35 s pre-rrna operon under the control of phage t7 promoter. the higher-order structure of the internal transcribed spacer 2 (its-2) region (between the 5.8 s and 25 s rrna sequence) in the pre-rrna molecule was investigated using a combination of enzymatic and chemical structural probes. the data were used to evaluate several structural models predicted by a minimum free-energy ... | 1990 | 2179564 |
| structure and expression of fyn genes in xenopus laevis. | by low stringency screening of a xenopus laevis oocyte cdna library with a probe prepared from the yes oncogene of the avian retrovirus y73, we have isolated clones encoding a 537 amino acid protein with 96% amino acid identity to the protein product of the human fyn proto-oncogene. in addition to the high degree of conservation at the amino acid sequence level, we also find a surprisingly high degree of sequence conservation between portions of the 5' untranslated regions of the frog and human ... | 1990 | 2179818 |
| characterization and expression of a xenopus ras during oogenesis and development. | we have characterized a cdna which contains the entire coding sequence of a xenopus laevis ras protein. the deduced amino acid sequence reveals a strong homology (92%) to human ki-ras 2b protein. ras expression has been studied both qualitatively and quantitatively during xenopus development. ras is expressed as a maternal mrna in oocytes and early embryos at a level up to 1.5 x 10(7) copies per mature oocyte, corresponding to the level of ras mrna found in 4 x 10(5) somatic growing cells. this ... | 1990 | 2184059 |
| axial patterning and the establishment of polarity in the frog embryo. | we review the early development of the frog xenopus laevis, concentrating on events that lead to the establishment of the body plan. recent molecular and embryological experiments suggest that peptide growth factors and homeobox genes interact to specify cell fates and pattern during early development of this vertebrate. | 1990 | 2186530 |
| membrane skeleton protein 4.1 in developing xenopus: expression in postmitotic cells of the retina. | membrane skeleton protein 4.1 plays a key role in modulating the interactions of spectrin, actin, and integral membrane proteins in erythroid and nonerythroid cells. we have investigated its structure and expression during embryonic development of xenopus laevis. an analysis of the complete 2758-nucleotide sequence and predicted translation of 801 amino acids (85.5 kda) of x. laevis oocyte protein 4.1 reveals that, within overlapping regions, oocyte protein 4.1 is 74% identical to a composite am ... | 1990 | 2186944 |
| k-ras oncogene expression in xenopus laevis. | a xenopus laevis homolog of mammalian kirsten-ras has been isolated from an oocyte cdna library. this ras clone has been used to examine the genomic representation and expression of ras in oocytes and embryos. the xenopus homolog of k-ras is a low-copy gene encoding a 2.6 kb mrna, which is present throughout oogenesis and embryonic development. dna sequence analysis indicates that xenopus and mammalian k-ras 2b are highly conserved at the mrna level (82%) and encode nearly identical proteins. it ... | 1990 | 2189109 |
| parvalbumin expression in normal and mutant xenopus embryos. | the levels and cellular distribution of pv were analyzed at the molecular level in normal and mutant xenopus laevis embryos. in developing tadpoles, pv protein expression was restricted to fast-twitch myotomal cells, as shown by immunofluorescence experiments with myosin isoform-specific monoclonal antibodies. both pv expressing and non-expressing myotomal cells can be cultured in vitro without neurons, and non-expressing cells have been shown to lack hybridizable levels of pv mrna. in a paralyz ... | 1990 | 2191556 |
| metal ion co-ordination in the dna binding domain of the yeast transcriptional activator gal4. | the structure of the dna binding domain of the yeast transcriptional activator gal4 was investigated by extended x-ray fine structure (e.x.a.f.s.). two samples of gal4 were studied, one containing cadmium as a structural probe (cd(ii)gal4) and the other containing the 'native' zinc (zn(ii)-gal4). the results suggest that the structure of the dna binding domain of gal4 contains a two metal ion cluster distinguishing it from the 'zinc finger' proteins typified by the xenopus laevis transcription f ... | 1990 | 2194836 |
| expression of spasmolysin (fim-a.1): an integumentary mucin from xenopus laevis. | in the past, a unique type of precursor for a secretory protein was discovered. it contains a central repetitive domain rich in threonine residues and terminal cysteine-rich domains. due to striking homologies of these terminal domains with pancreatic spasmolytic polypeptide, originally the name "prepro-spasmolysin" was proposed. here we show that the mature protein has a mw of about 130 kda, consisting of about 70% carbohydrate and 30% protein. similar o-linked glycoproteins have been found in ... | 1990 | 2196180 |
| transfer rna splicing endonuclease from xenopus laevis. | | 1990 | 2199763 |
| thyroxine-dependent modulations of the expression of the neural cell adhesion molecule n-cam during xenopus laevis metamorphosis. | during amphibian metamorphosis, a complete remodeling of the phenotype takes place under complex hormonal control whose final effectors are thyroid hormones. this process implies the activation of coordinated programs of cell death, proliferation, migration, adhesion and differentiation. inasmuch as the neural cell adhesion molecule n-cam is thought to play a central role in the control of morphogenetic processes, we have studied by immunohistofluorescence and immunoblots the patterns of express ... | 1990 | 2201513 |
| isolation of two different c-ets-2 proto-oncogenes in xenopus laevis. | | 1990 | 2201951 |
| occurrence of nonlymphoid leukocytes that are not derived from blood islands in xenopus laevis larvae. | previous immunohistochemical observations using the monoclonal antibody (xl-1) which recognizes all types of leukocytes in xenopus laevis revealed the occurrence of xl-1+ cells in the mesenchyme throughout the early larval body, before the appearance of any lymphocytes. the present experiments were performed to determine whether these leukocytes originate, like lymphocytes and red blood cells (rbcs), in the ventral blood islands (vbi) or the dorsolateral plate (dlp). for tracing the derivation o ... | 1990 | 2202604 |
| [the role of inducing factors in early embryonic development]. | in the field of early embryonic induction and differentiation we can observe an exponential increase of research activities over the last three years. the reasons for this rapid exploration are the application of powerful techniques of molecular biology and molecular genetics and the recent accumulation of knowledge about the close functional correlation between growth factors, embryonic induction factors, the products of oncogenes (or proto-oncogenes), and transcription factors. the highly prob ... | 1990 | 2204013 |
| [an immunohistochemical study of early embryogenesis in the clawed toad xenopus laevis by using monoclonal antibodies to intermediate filament proteins]. | distribution of cytokeratin epitopes was studied in x. laevis embryos at stages 10-25 using 5 monoclonal antibodies against proteins of the human and rat keratin filaments. specific staining was observed in chorda, outer layers of ectoderm and presumptive epidermis (late gastrula), and inner layer of presumptive epidermis. the cells of the stained zone (presumptive epidermis) were compressed while the cells of unstained zone (presumptive neuroectoderm) were extended tangentially. | 1990 | 2204015 |
| characterization of xenopus laevis cdna clones of the c-ets-1 proto-oncogene. | | 1990 | 2205841 |
| the xenopus laevis poly(a) binding protein is composed of multiple functionally independent rna binding domains. | a family of eukaryotic rna binding proteins is defined by the conserved rnp motif. the poly(a) binding protein has four such motifs. we report on the isolation and structural characterization of several variant cdna clones, as well as of a gene encoding this protein in xenopus laevis embryos. wild-type protein as well as truncated versions carrying isolated single motifs or artificial combinations of two and more such elements were characterized for their ability to bind specifically to rna homo ... | 1990 | 2209558 |
| transcription factor tfiiia stimulates dna supercoiling promoted by a fractionated cell-free extract from xenopus laevis. | an activity that can introduce negative supercoils into relaxed covalently closed dna molecules has been isolated from a xenopus laevis cell-free extract (s-150) and purified over 200-fold. the exogenous addition of atp, other ribonucleotides and deoxyribonucleotides, as well as nonhydrolyzable analogs, stimulate dna supercoiling which may occur by a pathway involving multiple protein components. dna supercoiling occurs in topological single steps and is inhibited by camptothecin and berenil, bu ... | 1990 | 2209588 |
| voltage-dependent action of valproate on potassium channels in frog node of ranvier. | the influence of the anti-epileptic drug, valproate, on k conductance (gk) was investigated in voltage-clamped ranvier nodes of xenopus laevis. a double pulse method was used in order to eliminate the effect of accumulation of potassium ions in the perinodal space, thus enabling the determination of the 'true' magnitude of gk. valproate (2.4 mm) had a voltage-dependent action on the magnitude of gk. with small step depolarizations more negative than about -50 mv, valproate increased gk (20 ms af ... | 1990 | 2209710 |
| elongation factor 1 alpha (ef-1 alpha) is concentrated in the balbiani body and accumulates coordinately with the ribosomes during oogenesis of xenopus laevis. | in xenopus laevis oocytes two distinct systems catalyze the mrna-dependent binding of aminoacyl trna to the a site of ribosomes. these systems are elongation factor 1 alpha (ef-1 alpha) and the 42s nucleoprotein particle. this particle is also implicated in the long-term storage of 5s rna and aminoacyl trna during early oogenesis. we report here that the ribosomes and the storage particles are distributed uniformly in the cytoplasm of previtellogenic (stage i) oocytes. in contrast, ef-1 alpha is ... | 1990 | 2210036 |
| formation and survival of a postsynaptic specialization in cultures of embryonic xenopus nerve and muscle cells. | the formation and survival of nerve-induced clusters of acetylcholine receptors (achrs) was monitored over a synaptogenic period of several days in cultures of myotomal muscle cells and spinal cord neurons derived from embryos of xenopus laevis. achrs were labeled with fluorescent alpha-bungarotoxin so that neurite-associated receptor patches (narps) could be viewed at daily intervals throughout the neuritic arbor of selected neurons. to avoid bleaching the narps and damaging the neurons, the in ... | 1990 | 2210043 |
| developmental and thyroid hormone-dependent regulation of pancreatic genes in xenopus laevis. | we have isolated and sequenced a cdna encoding xenopus laevis pancreatic trypsin, which has approximately 70% amino acid sequence identity to mammalian trypsinogen. northern blotting analysis shows that the trypsin gene is activated just before the tadpole starts to feed, reaches peak activity in the swimming tadpole (premetamorphosis), and is then repressed during prometamorphosis, attaining its lowest activity at the climax of metamorphosis. the same gene is then activated again in frogs but t ... | 1990 | 2210372 |
| an rna polymerase i termination site can stimulate the adjacent ribosomal gene promoter by two distinct mechanisms in xenopus laevis. | on the ribosomal genes of xenopus laevis, the t3 terminator is located approximately 60 bp upstream of the 5' boundary of the gene promoter. we have shown previously that mutation of the terminator simultaneously abolishes termination and impairs initiation by rna polymerase i. here, we show that the terminator influences the promoter by two distinct mechanisms. in one mechanism the terminator protects the promoter by preventing polymerase from reading through the initiation complex. in a second ... | 1990 | 2210376 |
| a cdna encoding human ribosomal protein s24. | we describe the isolation and nucleotide sequence of a cdna encoding the human 40s ribosomal subunit protein (r-protein) s24 (mr 15,425). human s24 is virtually identical to the r-protein encoded by a cloned xenopus laevis cdna previously identified as s19 [amaldi et al., gene 17 (1982) 311-316]. | 1990 | 2210388 |
| cytoplasmic transport of ribosomal subunits microinjected into the xenopus laevis oocyte nucleus: a generalized, facilitated process. | to study the biochemistry of ribonucleoprotein export from the nucleus, we characterized an in vivo assay in which the cytoplasmic appearance of radiolabeled ribosomal subunits was monitored after their microinjection into xenopus oocyte nuclei. denaturing gel electrophoresis and sucrose density gradient sedimentation demonstrated that injected subunits were transported intact. consistent with the usual subcellular distribution of ribosomes, transport was unidirectional, as subunits injected int ... | 1990 | 2211825 |
| hrpf, a human sequence-specific dna-binding protein homologous to xrpfi, a xenopus laevis oocyte transcription factor. | the identification in hela nuclei of a novel dna-binding protein, designated hrpf, is presented. this factor recognizes and binds a sequence of the xenopus laevis l14 ribosomal protein (r-p) gene promoter bound by the xenopus r-p transcription factor i (xrpfi). we show here that xrpfi and hrpf share a conserved dna-binding domain. we also present evidences suggesting that the two factors perform similar functions in the cell. we discuss the hypothesis that closely related factors might be involv ... | 1990 | 2216772 |
| a 140-base-pair repetitive sequence element in the mouse rrna gene spacer enhances transcription by rna polymerase i in a cell-free system. | we show that the repetitive 140-base-pair (bp) elements present in the spacer of mouse rrna genes function as enhancers for rna polymerase i. attachment of these elements to the rdna promoter stimulates rrna synthesis both in vivo and in vitro. the cis-activating effect of the spacer repeats is orientation-independent and increases with increasing numbers of the 140-bp elements. competition experiments demonstrate that the spacer repeats bind one or more of the transcription factors interaction ... | 1990 | 2217183 |
| sch 23390: d-1 modulation of oral dyskinesias induced in snakes by xenopus skin mucus. | the granular gland skin secretion of xenopus laevis induces seven involuntary oral dyskinesias and climbing behavior in the water snake nerodia sipedon. in a previous study the d-2 receptor antagonist, haloperidol (hal), selectively potentiated mucus-induced yawning and chewing but attenuated fixed gaping; other oral behaviors were unaffected; hal alone induced no dyskinesias and failed to modify mucus-induced decreases in tongue flicking, cage climbing and activity. as skin compounds have neuro ... | 1990 | 2217512 |
| aldosterone regulation of basolateral potassium channels in alveolar epithelium. | to reveal the regulatory mechanism of the mineralocorticoid aldosterone on basolateral k+ channels, the aldosterone-sensitive lung epithelium of xenopus laevis was investigated in ussing chambers under voltage-clamp conditions. transepithelial measurements were supplemented by current fluctuation analysis of short-circuit current noise in nonstimulated and aldosterone-stimulated lung tissues. the addition of 10(-6) m aldosterone stimulated short-circuit current from 11.3 +/- 2.0 to 27.8 +/- 4.8 ... | 1990 | 2221084 |
| structural and functional studies of the rat mitochondrial single strand dna binding protein p16. | the rat mitochondrial single strand dna binding protein (ssb) p16 was purified to apparent homogeneity by elution from single strand dna agarose with ethidium bromide. each monomer of p16 contains two tryptophan residues, and the intrinsic fluorescence from these residues is quenched upon binding to single strand polynucleotides. from fluorescence quench titrations of ligand to fixed amounts of dna lattice, a binding site size of 8 or 9 nucleotides per p16 monomer was found. measurement of the a ... | 1990 | 2221914 |
| spermiogenesis in xenopus laevis: from late spermatids to spermatozoa. | spermatogenesis is a complex morphogenetic process in which microfilaments and microtubules have been shown to play an important role. the last steps of xenopus spermatogenesis, i.e., the corkscrew shaping of the sperm head, have been followed to study actin and microtubule distribution by conventional and immunoelectron microscopy. during sperm head morphogenesis, actin is absent in the elongating spermatids, but it is present in the sertoli cells where results localized at the periphery of the ... | 1990 | 2223083 |
| phosphorus nuclear magnetic resonance of diverse phosvitin species. | 1. high resolution 31p nuclear magnetic resonance (nmr) spectra, with and without proton decoupling, of the principal egg phosphoproteins--phosvitins--of a bird (gallus gallus), an amphibian (xenopus laevis) and a fish (salmo gairdneri) were obtained. 2. the spectra were evaluated with special reference to available amino acid sequences and the major nmr resonance in all three spectra was assigned to phosphoserine clusters. 3. the resolution of numerous additional phosphorus resonances provides ... | 1990 | 2225770 |
| the induction of anterior and posterior neural genes in xenopus laevis. | we have investigated the interactions between mesoderm and ectoderm that result in the formation of a regionally differentiated nervous system in xenopus embryos. we have used genes expressed at different positions along the neural tube as regional markers of neural induction in both whole, and in experimentally manipulated embryos. by comparing transcription from the anterior marker, xif3, with that from the posterior marker, x1hbox6, and the general neural marker xif6, we have shown that the n ... | 1990 | 2226199 |
| transdifferentiation of larval xenopus laevis iris under the influence of the pituitary. | fragments of larval xenopus laevis dorsal iris implanted together with the pituitary into the tail fin transdifferentiate into neural retina. on the contrary, in the control experiments the implanted tissues, dorsal iris alone, pituitary, or dorsal iris with liver fragments, do not undergo any retinal transformation. | 1990 | 2226723 |
| the primary structure of rat ribosomal protein s7. | the amino acid sequence of the rat 40s ribosomal subunit protein s7 was deduced from the sequence of nucleotides in two recombinant cdnas and confirmed from the amino acid sequence of a cyanogen bromide peptide obtained from the protein. ribosomal protein s7 has 194 amino acids and has a molecular mass of 22,113. hybridization of the cdna to digest of nuclear dna suggests that there are 14-16 copies of the s7 gene. the mrna for the protein is about 725 nucleotides in length. rat s7 is homologous ... | 1990 | 2226813 |
| developmental changes in the half-life of acetylcholine receptors in the myotomal muscle of xenopus laevis. | 1. tail preparations, containing myotomal muscle and associated spinal cord, were isolated from embryos and tadpoles of xenopus laevis between stages 25 and 49 (1.15-12 days) and were pulse-labelled with 125i-alpha-bungarotoxin (125i alpha bt) so that the half-life (t1/2) of their acetylcholine receptors (achrs) could be estimated in organ culture. 2. for the entire population of achrs, estimates of t1/2 based on a single exponential decline in radioactivity (but see item 4 below) increased from ... | 1990 | 2231400 |
| repair and recombination of x-irradiated plasmids in xenopus laevis oocytes. | plasmid dna substrates were x-irradiated and injected into the nuclei of xenopus laevis oocytes. after incubation for 20 h, dna was recovered from the oocytes and analyzed simultaneously for repair and for intermolecular homologous recombination by electrophoresis and bacterial transformation. oocyte-mediated repair of dna strand breaks was observed with both methods. using a repair-deficient mutant escherichia coli strain and its repair-proficient parent as hosts for the transformation assay, w ... | 1990 | 2233720 |
| prenylation of mammalian ras protein in xenopus oocytes. | ras protein requires an intermediate of the cholesterol biosynthetic pathway for posttranslational modification and membrane anchorage. this step is necessary for biological activity. maturation of xenopus laevis oocytes induced by an oncogenic human ras protein can be inhibited by lovastatin or compactin, inhibitors of the synthesis of mevalonate, an intermediate of cholesterol biosynthesis. this inhibition can be overcome by mevalonic acid or farnesyl diphosphate, a cholesterol biosynthetic in ... | 1990 | 2233726 |
| chromosomal footprinting of transcriptionally active and inactive oocyte-type 5s rna genes of xenopus laevis. | the chromatin structure of the xenopus oocyte-specific 5s rrna genes was examined at high resolution in immature oocyte and somatic cell chromosomes by dnase i footprinting. on oocyte chromatin, where the genes are active, the cleavage preferences over the entire gene region showed a periodic pattern of sensitivity and were dramatically different from the patterns obtained with deproteinized dna or somatic cell chromatin. further, the normal binding site for tfiiia over the internal promoter reg ... | 1990 | 2235485 |
| dissection of the 16s rrna binding site for ribosomal protein s4. | the ribosomal protein s4 from escherichia coli is essential for initiation of assembly of 30s ribosomal subunits. we have undertaken the identification of specific features required in the 16s rrna for s4 recognition by synthesizing mutants bearing deletions within a 460 nucleotide region which contains the minimum s4 binding site. we made a set of large nested deletions in a subdomain of the molecule, as well as individual deletions of nine hairpins, and used a nitrocellulose filter binding ass ... | 1990 | 2207164 |
| guanosine modifications in runoff transcripts of synthetic transfer rna-phe genes microinjected into xenopus oocytes. | we have investigated whether unmodified yeast phenylalanine transfer rna as well as one of its precursors containing an intron of nineteen nucleotides in the anticodon (pre-trna-phe) can become substrates for selected trna modification enzymes present in a eukaryotic cell. this study was done by microinjecting into the cytoplasm of xenopus laevis oocytes transcripts completely deprived of the naturally occurring modified nucleotides; these were obtained in vitro from appropriate synthetic genes ... | 1990 | 2207154 |
| an integumentary mucin (fim-b.1) from xenopus laevis homologous with von willebrand factor. | we present a new protein from x. laevis skin termed "frog integumentary mucin b.1" (fim-b.1) with a general structure similar to fim-a.1 (formerly "spasmolysin"). the central region consisting of tandem repeats of 11 amino acid residues is probably a target for extensive o-glycosylation, whereas the c-terminal cysteine-rich domain shows pronounced homology with the c1-c2 domains and the c-terminal end of von willebrand factor. furthermore, we describe homology with antistasin, an anticoagulant p ... | 1990 | 2207068 |
| xenopus laevis alpha and beta thyroid hormone receptors. | | 1990 | 2236080 |
| expression of mammalian renal transporters in xenopus laevis oocytes. | we have injected mrna from rabbit renal cortex into xenopus oocytes and demonstrated the expression of renal carriers for na(+)-independent transport of l-phenylalanine and l-lysine and na(+)-dependent transport of l-alanine and succinate. maximal expression of renal amino acid transporters occurred 6-8 days following mrna injection. the proteins responsible for transport of these four substrates were translated from mrnas which are between 1.5 and 3.0 kb. this information serves as a starting p ... | 1990 | 2241165 |
| diversity in responses from endogenous and expressed mammalian receptors which cause chloride ion efflux from ovarian follicles of xenopus laevis. | inositol phosphates are produced in ovarian follicles of xenopus laevis on activation of endogenous acetylcholine receptors, which also stimulates ca2+ release and efflux of cl- ions detected electrophysiologically. inositol phosphates were not detectable on activation of endogenous angiotensin ii receptors which did, however, stimulate both a dose-dependent ca2+ efflux and a depolarizing current very similar in maximum size and other characteristics to those caused by acetylcholine action. in c ... | 1990 | 2241166 |
| cloning and sequencing of pou-boxes expressed in xenopus laevis neurula embryos. | | 1990 | 2235499 |
| serotonin-like immunoreactivity in the retina of the clawed frog xenopus laevis. | using an antiserum directed against serotonin, we have studied the morphology and distribution of serotonin-containing and serotonin-accumulating neurons in the retina of xenopus laevis. endogenous serotonin-like immunoreactivity was found in two classes of amacrine cell, one class of bipolar cell and a few centrifugal fibres. kainic acid-induced depletion of serotonin, under various conditions, enabled us to determine the distribution of stained bipolars, amacrine cells and centrifugal fibres w ... | 1990 | 2243244 |
| the enhancers and promoters of the xenopus laevis ribosomal spacer are associated with histones upon active transcription of the ribosomal genes. | the presence of histones on the enhancer-promoter region of the x.laevis ribosomal spacer has been studied in embryos at stage 40, where the ribosomal genes are actively transcribed. isolated tadpole nuclei were either fixed with formaldehyde or irradiated with uv laser to crosslink histones to dna. the purified protein-dna complexes were immunoprecipitated with antibodies to the histones h1, h2a and h4 and the dna fragments carrying the respective histones were analyzed for the presence of spac ... | 1990 | 2243781 |