| thyrotropin-releasing hormone facilitates display of reproductive behavior and locomotor behavior in an amphibian. | in the amphibian brain, thyrotropin-releasing hormone (trh) is present in many regions outside the hypothalamus. the functions of this extrahypothalamic trh however are unknown. we sought to determine whether trh or its metabolites altered reproductive behaviors (amplectic clasping behavior) or locomotor behaviors of the male south african clawed frog, xenopus laevis. trh-injected (100 micrograms; dorsal lymph sac injection) male xenopus displayed significantly fewer amplectic clasp attempts and ... | 1991 | 1906046 |
| a method for the demonstration of nadph-diaphorase activity in anuran species using unfixed retinal wholemounts. | the presence of nadph-diaphorase enzyme has been previously revealed in fixed mammalian retinal tissue (sagar, 1986). fixed retinae of bufo marinus and xenopus laevis failed to yield selective staining when reacted for nadph-diaphorase. satisfactory staining of retinal neurons was attained when the histochemical reaction was carried out in unfixed retinal wholemounts. the applied method included the following steps: 1) dissection of the fresh retina and the separation of the neural retina from a ... | 1991 | 1908262 |
| cell-surface receptor for ecotropic murine retroviruses is a basic amino-acid transporter. | the complementary dna sequence encoding the cell-surface receptor for ecotropic host-range murine retroviruses (ecor) shows that it contains 622 amino acids and 14 hydrophobic potentially membrane-spanning sequences. because this receptor occurs on many or all murine cells and is probably essential for viability of cultured fibroblasts, its normal function might be to transport an essential metabolite. we expressed ecor in xenopus laevis oocytes by injecting rna transcribed from the cloned cdna. ... | 1991 | 1908564 |
| [do the variations in water carbon dioxide pressure and ph have an effect on the nature of end products of protein catabolism, ammonia and urea, in the clawed frog xenopus laevis?]. | the effects of pco2 and ph changes in the ambient water on the nitrogen catabolism and the proportions of the excreted nitrogenous end products, ammonia and urea, were studied in the clawed frog, xenopus laevis, at 24 degrees c. in animals living in artificial fresh water, the exposure to a hypocapnic alkalosis (pco2 = 0.7 torr instead of 10 torr) did not entail any change in the nitrogen catabolism. in animals who lived in a water loaded with nacl and had therefore a higher oxygen consumption, ... | 1991 | 1913240 |
| dna-dependent phosphorylation of histone h2a.x during nucleosome assembly in xenopus laevis oocytes: involvement of protein phosphorylation in nucleosome spacing. | atp is required for physiological nucleosome alignment in chromatin reconstituted from high-speed nuclear supernatants of xenopus laevis oocytes. here we show that during in vitro nucleosome assembly the histone variant h2a.x becomes phosphorylated upon transfer onto dna, a process which is also observed in vivo. histone h2a.x phosphorylation increases in the early phase of the assembly reaction, reaching a steady state after approximately 16 min and is maintained with a half-life of the phospha ... | 1991 | 1915279 |
| structural analysis of the entire proopiomelanocortin gene of xenopus laevis. | in the pars intermedia of the pituitary the prohormone proopiomelanocortin (pomc) is tissue-specifically processed to, among other peptides, alpha-melanotropin (alpha msh). in the south african clawed toad xenopus laevis this hormone mediates the process of background adaptation: release of alpha-msh causes darkening of the animal, while inhibition of alpha-msh release results in a pale toad. elevated release of alpha-msh coincides with a higher rate of pomc gene transcription. the present study ... | 1991 | 1915355 |
| nuclear pore complex glycoprotein p62 of xenopus laevis and mouse: cdna cloning and identification of its glycosylated region. | cdna clones for nuclear pore complex glycoprotein p62 of two distantly related species, mouse and xenopus laevis, were isolated. antibodies raised against recombinant murine p62 react on protein blots with p62 of both species and decorate pore complexes. analysis of the predicted protein sequence indicates that vertebrate p62 is organized into two structurally different regions. the entire carboxy-terminal half (86.7% identical amino acids) and the amino-terminal 56 amino acids (62.5% identity) ... | 1991 | 1915419 |
| furrow-related contractions are inhibited but furrow-unrelated contractions are not affected in af mutant eggs of xenopus laevis. | in embryos from af mutant females of xenopus laevis, the cleavage furrows stayed on the surface and cytoplasmic divisions did not take place at all, while nuclear divisions continued (kubota et al., 1991). to gain insights into the roles of the normal product of af on early development, contractile events which have been observed in the period from fertilization until first cleavage in wild-type eggs were examined in af mutant eggs. activation waves, activation contraction, and surface contracti ... | 1991 | 1916014 |
| tunicamycin-inducible polypeptide synthesis during xenopus laevis embryogenesis. | tunicamycin treatment of xenopus laevis embryos enhanced the synthesis of a specific set of polypeptides with molecular masses of 98, 78, 59 and 58 kda. the 78-kda polypeptide was tentatively identified as glucose-regulated protein (grp) 78 on the basis of molecular mass, pl (5.2), and tunicamycin inducibility, which took place upon treating embryos after the midblastula transition (mbt). the synthesis of a polypeptide with this electrophoretic mobility was detected but was not tunicamycin-induc ... | 1991 | 1916065 |
| internal deletions in human interleukin-6: structure-function analysis. | by cdna mutagenesis, we have constructed internal and c-terminal deletions (delta 21-51, delta 52-97, delta 97-104, delta 127-174, delta 97-184 and delta 134-184) in human interleukin-6 (hil-6). all those deletion-carrying hil-6 (delta hil-6) proteins were then produced in xenopus laevis oocytes and examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (sds-page). the results show that, at least in frog oocytes, the first potential n-glycosylation site (asn45) is utilized exclusi ... | 1991 | 1916293 |
| expression of two nonallelic type ii procollagen genes during xenopus laevis embryogenesis is characterized by stage-specific production of alternatively spliced transcripts. | the pattern of type ii collagen expression during xenopus laevis embryogenesis has been established after isolating specific cdna and genomic clones. evidence is presented suggesting that in x. laevis there are two transcriptionally active copies of the type ii procollagen gene. both genes are activated at the beginning of neurula stage and steady-state mrna levels progressively increase thereafter. initially, the transcripts are localized to notochord, somites, and the dorsal region of the late ... | 1991 | 1918153 |
| novel applications of acrylamide for cryosectioning of isolated cells, tissues, and arthropods. | cross-linked and uncross-linked acrylamide polymers were used to alleviate technical difficulties in cryosectioning and autoradiographic processing of marine arthropods (pycnogonum litorale), larval insect tissues (sarcophaga bullata), and amphibian (xenopus laevis) oocytes. rapidly polymerized cross-linked acrylamide was used to prepare sections from an animal with a hard thick cuticle, p. litorale. fragmentation and compression artifacts caused by tissue density differences were avoided and in ... | 1991 | 1918945 |
| subdivisions of the terminal nerve in xenopus laevis. | the majority of recent studies on the terminal nerve (nt) in various vertebrates either involved tracer injections into the nasal cavity or made use of the lhrh-/fmrfamide-like immunoreactivity (ir) of a portion of its fibers. the present investigation was designed to determine the extent of overlap between data rendered by the two methods in xenopus. the findings reveal no overlap of nt projections visualized by the two experimental techniques. this result sheds doubt on the validity of current ... | 1991 | 1919462 |
| identification and functional analysis of the nuclear localization signals of ribosomal protein l25 from saccharomyces cerevisiae. | the regions of the large subunit ribosomal protein l25 from saccharomyces cerevisiae responsible for nuclear localization of the protein were identified by constructing fusion genes encoding various segments of l25 linked to the amino terminus of beta-galactosidase. indirect immunofluorescence of yeast cells expressing the fusions demonstrated that amino acid residues 1 to 17 as well as 18 to 41 of l25 promote import of the reporter protein into the nucleus. both nuclear localization signal (nls ... | 1991 | 1920406 |
| coordinate estrogen-regulated instability of serum protein-coding messenger rnas in xenopus laevis. | estrogen causes the cytoplasmic destabilization of albumin and gamma-fibrinogen mrna in xenopus laevis liver. the purpose of the present study was to determine whether mrna destabilization is a generalized phenomenon in response to estrogen, or whether this process is restricted to a particular class of mrnas. to address this, we have expanded our bank of serum protein-coding cdna clones to include transferrin, the second protein of inter-alpha-trypsin inhibitor and clone 12b, for which there is ... | 1991 | 1922078 |
| in vitro binding of the purified hormone-binding subunit of the estrogen receptor to oligonucleotides containing natural or modified sequences of an estrogen-responsive element. | estrogen receptor (er) was purified from calf uterus by immunoaffinity chromatography in the absence of the ligand. the purified er consists of a mixture of monomer and homodimer forms of 67-kda hormone-binding subunit (no 90-kda heat shock protein is present). the purified er was incubated with a 32p-labeled 61-basepair oligonucleotide containing the sequence of the estrogen response element (ere) of the xenopus laevis a2 vitellogenin gene. dna mobility shift assays showed formation of specific ... | 1991 | 1922088 |
| coordinate regulation of fibrinogen subunit messenger rna levels by glucocorticoids in primary cultures of xenopus liver parenchymal cells. | fibrinogen synthesis is specifically induced by a synthetic glucocorticoid, dexamethasone, in primary liver parenchymal cell cultures of the frog xenopus laevis. here we demonstrate that this increase in the level of fibrinogen protein production is accompanied by an induction in the three mrnas coding for the fibrinogen subunits, designated a alpha, b beta, and gamma. the stimulation of fibrinogen mrna levels appears to be mediated by the glucocorticoid receptor, because 1) the dose-response re ... | 1991 | 1922091 |
| germ cell-specific expression of a gene encoding eukaryotic translation elongation factor 1 alpha (eef-1 alpha) and generation of eef-1 alpha retropseudogenes in xenopus laevis. | we have studied by in situ hybridization the expression of the genes encoding the somatic form and the oocyte form of xenopus laevis eef-1 alpha. the somatic form of eef-1 alpha (eef-1 alpha s) mrna is virtually undetectable in male and female germ cells of the adult gonad but is very abundant in embryonic cells after the neurula stage. in contrast, another form of eef-1 alpha (eef-1 alpha o) mrna is highly concentrated in oogonia and in previtellogenic oocytes but is undetectable in eggs and em ... | 1991 | 1924391 |
| morphological and immunological changes in the spleen of xenopus laevis during metamorphosis. | | 1991 | 1925006 |
| biological structures imaged in a hybrid scanning transmission electron microscope and scanning tunneling microscope. | a hybrid scanning transmission electron microscope (stem) and scanning tunneling microscope (stm) is described which allows simultaneous imaging of biological structures adsorbed to electron-transparent specimen supports in both modes of scanning microscopy, as demonstrated on uncoated phage t4 polyheads. we further discuss the reproducibility and validity of height data obtained from stm topographs of biomacromolecules and present raw data from topographs of freeze-dried, metal-coated nuclear e ... | 1991 | 1926633 |
| microglia in tadpoles of xenopus laevis: normal distribution and the response to optic nerve injury. | we have studied the distribution of microglia in normal xenopus tadpoles and after an optic nerve lesion, using a monoclonal antibody (5f4) raised against xenopus retinas of which the optic nerves had been cut 10 days previously. the antibody 5f4 selectively recognizes macrophages and microglia in xenopus. in normal animals microglia are sparsely but widely distributed throughout the retina, optic nerve, diencephalon and mesencephalon (other regions were not examined). after crush or cut of an o ... | 1991 | 1928746 |
| glycoconjugate histochemistry of xenopus laevis fundic gland with special reference to mucous neck cells during development. | mucous neck cells (mncs) of the fundic gland are phylogenetically thought to have first appeared in amphibians. we studied the origin and differentiation of mncs in fundic glands of xenopus laevis. by means of lectin histochemical methods using griffonia simplicifolia agglutinin-ii (gsa-ii), mncs were detected specifically in fundic glands of adult x. laevis. mucous granules of mncs were labeled by gsa-ii-colloidal gold (cg) staining. other cells such as surface mucous cells (smcs), oxynticopept ... | 1991 | 1928755 |
| mapping the polarity profiles of general anesthetic target sites using n-alkane-(alpha, omega)-diols. | the effects of the homologous series of n-alkane-(alpha, omega)-diols have been studied on the inhibition of the purified firefly luciferase enzyme from photinus pyralis, the inhibition of the purified bacterial luciferase enzyme from vibrio harveyi, and the induction of general anesthesia in xenopus laevis tadpoles. all but one of the diols tested were found to be reversible general anesthetics. the diols inhibited firefly luciferase by competing with its normal substrate firefly luciferin, and ... | 1991 | 1931978 |
| the switch from larval to adult globin gene expression in xenopus laevis is mediated by erythroid cells from distinct compartments. | the transition of hemoglobins during metamorphosis of xenopus laevis involves replacement of the larval erythrocytes by adult ones, suggesting that the developmental control of this event depends upon the growth characteristics of the precursor cells. to identify the erythroid precursor cells and to investigate their developmental fate, we analyzed the distribution of stage-specific globin mrnas by northern blotting in dorsal and ventral fragments of stage 32 embryos after in vitro culture as we ... | 1991 | 1935695 |
| purification and cdna cloning of xenopus laevis skin peptidylhydroxyglycine n-c lyase, catalyzing the second reaction of c-terminal alpha-amidation. | the alpha-amidation of glycine-extended peptides is a two-step reaction catalyzed by peptidylglycine alpha-hydroxylating monooxygenase (phm) and peptidylhydroxyglycine n-c lyase (phl). phl was purified to homogeneity from xenopus laevis skin and its partial amino acid sequence (including the n-terminal 35 residues) was determined. it was found that the cdna codes for a 935-residue precursor protein (ae-iii protein), containing the phm and phl sequences at its n terminus and c terminus, respectiv ... | 1991 | 1935950 |
| mechanisms of the tetrahydroaminoacridine effect on action potential and ion currents in myelinated axons. | 9-amino-1,2,3,4-tetrahydroacridine (tha) in the range of 10-300 microm was shown to prolong the action potential in myelinated nerve fibres of xenopus laevis. voltage-clamp experiments showed that tha, besides reducing the na+ and the k+ current, modified the na+ current inactivation and the k+ current activation. the effects were frequency dependent. quantitative models were developed and used in computer simulations of the tha effect on the action potential. the computations showed that the ob ... | 1991 | 1936128 |
| posttranscriptional regulation of c-myc rna during early development of xenopus laevis. | the remarkable stability of c-myc during oogenesis contrasts with its degradation during the early developmental period in xenopus laevis. three evolutionary conserved motifs found in the 3'-untranslated region of xenopus c-myc rnas have been analyzed for a possible role in c-myc rna degradation. no specific degradation was observed when these sequences were cloned downstream of a reporter gene and the corresponding rnas were injected into fertilized eggs. the relation between polyadenylation an ... | 1991 | 1936260 |
| cellular mechanism of metformin action. | activation of the insulin receptor tyrosine kinase and tyrosine phosphorylation of intracellular substrates are important steps in insulin signalling. in order to elucidate the cellular mechanism of action of metformin (nn'dimethylbiguanide) we have focused towards the effects of metformin on the insulin receptor kinase, the phosphorylation cascade and the biological effect of insulin. since annexins (lipocortins) have been recently recognized as substrates of several tyrosine kinases we have in ... | 1991 | 1936468 |
| the cloning and characterization of a maternally expressed novel zinc finger nuclear phosphoprotein (xnf7) in xenopus laevis. | we report the cloning of a cdna (xnf7) coding for a maternally expressed xenopus protein that becomes highly enriched in nuclei of the central nervous system during later development and in nuclei of adult brain. the protein also shows stage-specific nuclear/cytoplasmic partitioning and phosphorylation that may be related to its function. in addition, it binds to double-stranded dna in vitro. the conceptual protein produced by the xnf7 clone contains several acidic domains, a novel zinc finger d ... | 1991 | 1936552 |
| characterization of the ooplasmic factor inducing decondensation of and protamine removal from toad sperm nuclei: involvement of nucleoplasmin. | immunohistochemical studies with antiserum against the protamines of the toad, bufo japonicus, revealed that the sperm nucleus loses protamines within 5 min after entry into the egg. likewise, lysolecithin-permeabilized sperm incubated with the egg extract lose the protamines within 1 min, accompanied by nuclear decondensation. the activities that induce both protamine removal and decondensation in sperm nuclei were found in extracts from growing and mature oocytes and pregastrula embryos, but n ... | 1991 | 1936566 |
| a xenopus laevis creatine kinase isozyme (ck-iii/iii) expressed preferentially in larval striated muscle: cdna sequence, developmental expression and subcellular immunolocalization. | a cdna containing the nearly complete coding sequence of ck-iii subunit of x. laevis was isolated, sequenced and further identified by comparing the tissue distribution of ck-iii/iii isozyme with that of its messenger. comparison of ck-iii deduced amino acid sequence with other ck sequences published reveals its close homology to m-ck subunits. results using both cdna probes and monoclonal antibodies specific for ck-iii subunits indicate that the appearance and the accumulation of ck-iii occur i ... | 1991 | 1936981 |
| xubf contains a novel dimerization domain essential for rna polymerase i transcription. | xenopus laevis upstream binding factor (xubf) is an rna polymerase i transcription factor that is required for formation of the stable initiation complex. the 701-amino-acid protein contains three regions of homology to the chromosomal protein hmg1 (the hmg boxes), which act in comparative independence to cause dna binding. dna binding is augmented by a 102-residue amino-terminal domain that causes xubf to form dimers. the dimerization domain is bipartite in structure, consisting of two regions ... | 1991 | 1936987 |
| xp1 and xp4. p-domain peptides expressed in xenopus laevis stomach mucosa. | two different precursors for secretory polypeptides from the stomach of xenopus laevis have been characterized by cdna cloning. both mature polypeptides are potential candidates for gastrointestinal growth factors. one, xp1, is the x. laevis homologue of the ps2 gene product consisting only of a single p-domain, whereas the second, xp4, is a novel polypeptide formed by four p-domains arranged in tandem. northern analysis detected both transcripts in the stomach but not in the skin or the brain. ... | 1991 | 1939167 |
| the astacin family of metalloendopeptidases. | molecular cloning of a human intestinal brush border metalloendopeptidase (n-benzoyl-l-tyrosyl-p-aminobenzoic acid hydrolase, pph) and a mouse kidney brush border metalloendopeptidase (meprin a) has revealed 82% identity in the nh2-terminal amino acid sequences (198 residues) of the mature enzymes. furthermore, searching of protein sequence data bases with the inferred peptide sequences as probes revealed strong similarities to astacin, a crayfish digestive protease, and an nh2-terminal domain o ... | 1991 | 1939172 |
| the influence of denervation on grafted hindlimb regeneration of larval xenopus laevis. | the aim of the present research is to ascertain whether in larval xenopus laevis nerve-independence for the regeneration of early stage limbs and nerve-dependence of late stage limbs observed in a previous work (filoni and paglialunga, '90) is related to extrinsic (systemic) factors or to intrinsic changes taking place in the limb cells themselves during development. in this paper the regenerative capacity of early and late stage hindlimbs under the same extrinsic conditions, insofar as both are ... | 1991 | 1940823 |
| lens formation from the cornea following implantation into hindlimbs of larval xenopus laevis: the influence of limb innervation and extent of differentiation. | corneal fragments of larval xenopus laevis at stage 48 (according to nieuwkoop and faber, '56), were implanted into sham denervated unamputated hindlimbs, denervated unamputated hindlimbs, amputated and sham denervated hindlimbs, and amputated and denervated hindlimbs of larvae at stages 52 and 57. the results show that unamputated limbs at stage 52, either innervated or denervated, manifest a weak capacity to promote the first lens-forming transformations of the outer cornea. this capacity is a ... | 1991 | 1940824 |
| an epizootic of cutaneous zygomycosis in cultured dwarf african clawed frogs (hymenochirus curtipes) due to basidiobolus ranarum. | morbidity and mortality approaching 100% occurred in dwarf african clawed frogs (hymenochirus curtipes) from a culture facility in central california. moribund frogs exhibited preference for a terrestrial environment rather than their normal aquatic environment. affected animals had a slight pallor of the integument but were otherwise grossly unremarkable. microscopic examination revealed a fungal infection of the integument primarily characterized by the presence of surface and intra-epidermal ... | 1991 | 1941429 |
| developmentally regulated alternative splicing in the xenopus laevis c-myc gene creates an intron-1 containing c-myc rna present only in post-midblastula embryos. | two distinct c-myc rna classes have been identified in xenopus laevis, presumably expressed from the duplicated c-myc locus (1, 6). the major xenopus c-myc transcripts arise from sites termed p1 and p2 similarly to those of the mammalian c-myc genes. i have used a cloned xenopus c-myc gene to examine the regulated pattern of expression from this gene during early xenopus embryogenesis. analysis of the pattern of transcript processing indicates that not only are p1 and p2 differentially active du ... | 1991 | 1945855 |
| acetylaminofluorene and aminofluorene adducts inhibit in vitro transcription of a xenopus 5s rna gene only when located on the coding strand. | unique n-acetyl-2-aminofluorene (aaf) or 2-aminofluorene (af) adducts were introduced into the xenopus borealis somatic 5s rna gene between the intragenic control region and the transcription termination site. the effects of these bulky adducts on transcription were studied in a cell-free extract derived from xenopus laevis oocytes. aaf and af adducts inhibit transcription only when they are on the template strand, whereas transcription passes through these adducts when they are placed on the no ... | 1991 | 1946373 |
| cloning and expression of cdna for a na/pi cotransport system of kidney cortex. | a cdna library from rabbit kidney cortex was screened for expression of na-dependent transport of phosphate (pi) using xenopus laevis oocytes as an expression system. a single clone was eventually isolated (designated napi-1) that stimulated expression of na/pi cotransport approximately 700-fold compared to total mrna. the predicted sequence of the na/pi cotransporter consists of 465 amino acids (relative molecular mass, 51,797); hydropathy profile predictions suggest six (possibly eight) membra ... | 1991 | 1946375 |
| lumbar lateral motor columns and hindlimbs of two xenopus laevis chromosome mosaics. | two chromosome mosaic xenopus laevis, one tadpole and one metamorphic animal, both with different sizes of neurons on the left and right sides of their brains and spinal cords, have left and right lumbar lateral motor columns (l-lmcs) of equal lengths but composed of strikingly different numbers of motoneurons (40% fewer motoneurons on the side composed of larger cells). one portion of the lumbar cord in the metamorphic animal is bilaterally symmetrical; the cells on both sides are small and the ... | 1991 | 1951137 |
| primary structure of the two variants of xenopus laevis mtssb, a mitochondrial dna binding protein. | the primary structure of the single-stranded dna binding protein from xenopus laevis oocyte mitochondria (mtssb) has been determined by edman degradation of the intact molecule and peptides derived from partial alpha-chymotrypsin proteolysis and enzymatic cleavage with trypsin and endoproteinase glu-c. the native mtssb is composed of two related polypeptide chains, mtssbs and mtssbr. the sequence of mtssbs consists of 129 amino acids with a calculated molecular mass of 14,627 da. comparison of t ... | 1991 | 1952953 |
| teratogenesis, toxicity, and bioconcentration in frogs exposed to dieldrin. | teratogenesis, acute and chronic toxicity, growth and bioconcentration were investigated in various life stages (embryos, tadpoles, juveniles, adults) of the frogs xenopus laevis (african clawed frog), rana catesbeiana (bullfrog) and rana pipiens (leopard frog) exposed to aqueous dieldrin in static-renewal and flow-through systems in a study on the development of wildlife-based water quality criteria. r. catesbeiana was the most sensitive tadpole in acute tests; x. laevis was the most sensitive ... | 1991 | 1953024 |
| high yield purification of active transcription factor iiia expressed in e. coli. | transcription factor iiia (tfiiia), a sequence-specific dna-binding protein from xenopus laevis, is a zinc finger protein required for transcription of 5s rrna genes by rna polymerase iii. we describe the purification and characterization of recombinant tfiiia (rectfiiia) expressed in e. coli. rectfiiia was purified to greater than 95% homogeneity at a yield of 2-3 milligrams per liter of bacterial culture. this purified protein protects the internal control region of a 5s rrna gene from dnase i ... | 1991 | 1956778 |
| interaction of xenopus lamins a and lii with chromatin in vitro mediated by a sequence element in the carboxyterminal domain. | morphological data suggest an interaction of the nuclear lamina with chromatin which markedly changes during the cell cycle. to study the molecular basis of this interaction we developed a novel lamin/chromatin binding assay that quantitated the binding of soluble, radiolabeled lamins to minichromosomes assembled in xenopus laevis oocyte nuclear extracts. lamins were derived from couple in vitro transcription and translation of the corresponding cdnas. chromatin binding was detected by monitorin ... | 1991 | 1959562 |
| substitute anions and the chloride conductance of frog muscle: effects of chlorate and bromate on steady-state values and kinetics. | voltage-clamp experiments have been used to study the effects of external nitrate, chlorate and bromate on the chloride conductance of sarcolemma of xenopus laevis. nitrate reduces inward current (chloride efflux), but less potently than does thiocyanate [vaughan (1987) pflügers arch 410:153-158] and does not affect conductance kinetics. as its concentration is increased the blocking effect of nitrate saturates; at a nitrate mole fraction of 0.6 the anion conductance is reduced to about 50% and ... | 1991 | 1961685 |
| functional expression cloning and characterization of the hepatocyte na+/bile acid cotransport system. | liver parenchymal cells continuously extract high amounts of bile acids from portal blood plasma. this uptake process is mediated by a na+/bile acid cotransport system. a cdna encoding the rat liver bile acid uptake system has been isolated by expression cloning in xenopus laevis oocytes. the cloned transporter is strictly sodium-dependent and can be inhibited by various non-bile-acid organic compounds. sequence analysis of the cdna revealed an open reading frame of 1086 nucleotides coding for a ... | 1991 | 1961729 |
| expression of gata-binding proteins during embryonic development in xenopus laevis. | proteins that recognize the core sequence gata are important regulators of hematopoietic-specific gene transcription. we have characterized cdnas encoding the xenopus laevis homologues of three related transcription factors, designated gata-1, -2, and -3. comparative sequence analysis reveals strong conservation of the zinc-finger dna-binding domain among all vertebrate gata-binding proteins. gata-2 and gata-3 polypeptides are homologous throughout their entire sequences, whereas gata-1 sequence ... | 1991 | 1961730 |
| homologous recombination catalyzed by a nuclear extract from xenopus oocytes. | xenopus laevis oocytes efficiently recombine linear dna injected into their nuclei (germinal vesicles). this process requires homologous sequences at or near the molecular ends. here we report that a cell-free extract made from germinal vesicles is capable of accomplishing the complete recombination reaction in vitro. like the in vivo process, the extract converts the overlapping ends of linear substrate molecules into covalently closed products. establishment of this cell-free system has allowe ... | 1991 | 1961753 |
| a homolog of the armadillo protein in drosophila (plakoglobin) associated with e-cadherin. | three cytoplasmic proteins, called catenins, bind to the cytoplasmic tail of the epithelial cell-cell adhesion molecule e-cadherin. the complementary dna sequence was determined for the 92-kilodalton beta catenin of xenopus laevis. the sequence is homologous to mammalian plakoglobin, a protein of desmosomal and zonula adherens cell junctions, and to the plakoglobin homolog in drosophila melanogaster, the product of the segment polarity gene armadillo. a monoclonal antibody to bovine plakoglobin ... | 1991 | 1962194 |
| a glucocorticoid response element enhances transcription of a methionine trna gene in cis and trans. | in vitro transcription experiments using a xenopus laevis cell-free extract have demonstrated that a dna fragment containing a glucocorticoid response element (gre) significantly enhances the expression of a methionine trna gene. this stimulation can be observed when the element is located in cis or trans. in the cis configuration, the element can be located 2900 basepairs from the gene and still display transcriptional enhancement. in trans, the enhancement can occur at a low element to templat ... | 1990 | 1963472 |
| neurohypophysial hormones and steroidogenesis in the interrenals of xenopus laevis. | the influence of arginine vasotocin (avt) on the interrenal secretion of the clawed toad (xenopus laevis) was studied combining in vivo and in vitro experiments. in vivo: a single injection of 3 nmol avt per 100 g body weight was given, and the concentrations of corticosterone and aldosterone in the serum were measured after 1, 3, 6, 12, and 24 hr. the serum levels of both steroids remained elevated over 6 hr and declined to normal levels within 12 hr. the increase of the aldosterone concentrati ... | 1990 | 1963609 |
| endocytosis via coated pits mediated by glycoprotein receptor in which the cytoplasmic tail is replaced by unrelated sequences. | rat 6 fibroblast cell lines expressing wild-type chicken liver glycoprotein receptor (chl) or chimeric receptors with alternate cytoplasmic tails were produced to study the role of the cytoplasmic tail in mediating receptor localization in coated pits and endocytosis of ligand. cells expressing chl or cells expressing a hybrid receptor that contains the cytoplasmic tail of the asialoglycoprotein receptor display high-efficiency endocytosis of n-acetylglucosamine-conjugated bovine serum albumin i ... | 1990 | 1963794 |
| assembly of transcriptionally active chromatin in vitro: a possible role for topoisomerase ii. | some models of in vitro chromatin assembly suggest a biphasic molecular mechanism. the first phase, nucleosome formation, is comprised of the formation of histone-dna complexes which mature into a canonical nucleosome structure. the second phase represents the process by which these nucleosomes become properly spaced with a regular periodicity on the dna. in this report, we examine the role of dna topoisomerases in the latter phase of chromatin assembly. to study this process, we use a xenopus l ... | 1990 | 1964075 |
| two types of intrinsic muscarinic responses in xenopus oocytes. i. differences in latencies and 45ca efflux kinetics. | oocytes of 40% of xenopus laevis frogs respond to acetylcholine (ach). oocytes of the majority of responders exhibit the common two-component depolarizing muscarinic response (mean amplitude of the rapid component, 54 na). oocytes of approximately 10% of the responders ("variant" donors) exhibit a muscarinic response characterized by a very large transient, rapid current (mean amplitude 1242 na, reversal potential -33 mv). responses in oocytes of variant donors exhibit further qualitative differ ... | 1990 | 1964211 |
| characterization of msh/acth-like immunoreactivity in sciatic nerves of xenopus laevis by immunocytochemistry, western blotting and radioimmunoassay. | previous studies have indicated that rat neurofilament protein may contain an endogenous msh-like epitope with neuroregenerative properties. the presence of such an epitope has now been studied in nerve tissue from xenopus laevis. western blot analyses of sciatic nerve tissue using an assortment of sequence-specific msh/acth antisera revealed the presence of two major immunoreactive protein bands of 52 and 50 kda, which contained a mid-region msh-like epitope. weaker staining occurred in another ... | 1990 | 1964445 |
| [reconstitution of rabbit brain gaba binding protein (receptor) on xenopus oocytes]. | gurdon's xenopus laevis oocyte translation system has been extensively employed to investigate the molecular biology of gamma-aminobutyric acid (gaba) receptors in the brains of embryonic chick, rat, etc. as gaba and its receptor may play a role in the pathogenesis of hepatic encephalopathy and a rabbit model of fulminant hepatitis has been established, we reconstituted the rabbit model of fulminant hepatitis has been established, we reconstituted the rabbit brain gaba binding protein (receptor) ... | 1990 | 1965592 |
| protein phosphatase activities in vivo in xenopus laevis oocyte: inhibition by okadaic acid. | protein phosphatase activities were analyzed in vivo in xenopus oocytes. the dephosphorylation of microinjected beta casein was inhibited when the tumor promoter okadaic acid was microinjected into oocytes. inhibition was dose dependent and reversible; 50% of activity was recovered 15-30 minutes after microinjection. | 1990 | 1965791 |
| activin as a cell differentiation factor. | activin, originally discovered as a polypeptide hormone that is capable of stimulating follicle-stimulating hormone secretion from pituitary cells in vitro, has recently been found to have a much wider range of biological activities. there are a number of reports of activin action as a cell differentiation factor on various types of cells rather than as a modulator of hormone secretion, as predicted initially, based on its structural similarity to transforming growth factor-beta. studies of the ... | 1990 | 1966558 |
| expression of class ii major histocompatibility complex antigens on adult t cells in xenopus is metamorphosis-dependent. | class ii major histocompatibility complex (mhc) antigens are expressed predominantly on b lymphocytes and macrophages of tadpoles of the south african clawed frog, xenopus laevis, as is the pattern in lymphocyte populations of most mammals. however, unlike most mammals, young postmetamorphic frogs show expression of class ii mhc antigens on a high proportion of thymocytes and most peripheral t and b lymphocytes. using the j-strain of xenopus and the anticlass ii monoclonal antibody, 14a2, we hav ... | 1990 | 1967017 |
| npxy, a sequence often found in cytoplasmic tails, is required for coated pit-mediated internalization of the low density lipoprotein receptor. | rapid internalization of the cell surface low density lipoprotein (ldl) receptor requires the first 22 amino acids of the cytoplasmic domain (residues 790-811), which must include an aromatic residue at position 807. in the human ldl receptor, this position is part of a tetrameric sequence, npvy. a similar tetramer, npxy (where x stands for any amino acid), is conserved in ldl receptors from six species (including xenopus laevis) and in two members of the ldl receptor gene family, human ldl rece ... | 1990 | 1968060 |
| a slowly inactivating potassium current in native oocytes of xenopus laevis. | membrane currents were recorded in voltage-clamped oocytes of xenopus laevis in response to voltage steps. we describe results obtained in oocytes obtained from one donor frog, which showed an unusually large outward current upon depolarization. measurements of reversal potentials of tail currents in solutions of different k+ concentration indicated that this current is carried largely by k+ ions. it was strongly reduced by extracellular application of tetraethylammonium, though not by ba2+ or 4 ... | 1990 | 1968644 |
| [modification of pattern formation along the anterior-posterior axis by introduction of excess amount of homeobox mrnas in xenopus laevis embryos]. | | 1990 | 1969669 |
| expression of rat liver canalicular sulfate carrier in xenopus laevis oocytes. | poly(a)+ rna (mrna)extracted from rat liver was injected into xenopus laevis oocytes and the expression of sulfate transport was determined by measuring [35s] sulfate uptake. compared to water-injected oocytes, which exhibited virtually no sulfate uptake, injection of rat liver mrna resulted in a time- and dose-dependent increase in uptake of sulfate. depending on the method used for the isolation of the mrna, sulfate uptake was stimulated after injection (40 ng after 6 days) between 8- and 72-f ... | 1990 | 1970568 |
| amphibian experimental systems: developmental neurobiology and behavioral endocrinology in the clawed frog, xenopus laevis. | | 1990 | 1974779 |
| xenopus laevis oocytes injected with mammalian pituitary mrna as a model system for study of thyrotropin-releasing hormone action. | | 1990 | 1974807 |
| neural expression of the xenopus homeobox gene xhox3: evidence for a patterning neural signal that spreads through the ectoderm. | the xenopus laevis homeobox gene xhox3 is expressed in the axial mesoderm of gastrula and neurula stage embryos. by the late neurula-early tailbud stage, mesodermal expression is no longer detectable and expression appears in the growing tailbud and in neural tissue. in situ hybridization analysis of the expression of xhox3 in neural tissue shows that it is restricted within the neural tube and the cranial neural crest during the tailbud-early tadpole stages. in late tadpole stages, xhox3 is onl ... | 1990 | 1974841 |
| genes and mechanisms involved in early embryonic development in xenopus laevis. | our laboratory is studying genes involved in the regulation of the balance between cell growth and differentiation during embryonic development in xenopus. we have analyzed the developmental expression of the proto-oncogenes c-myc, and kiras 2b, the proliferating cell nuclear antigen (pcna), and the tumor suppressor gene p53. these genes, usually expressed during cell proliferation, are expressed in the oocyte in large quantities, but the majority of their maternal rnas are degraded by the gastr ... | 1990 | 1975504 |
| glycine stimulates calcium-independent release of 3h-gaba from isolated retinas of xenopus laevis. | a perfusion system was used to monitor the release of [3h]-gaba from isolated retinas of xenopus laevis. measurable release was stimulated by glycine at concentrations as low as 200 microm. glycine-stimulated release was blocked by strychnine, and was not reduced in "calcium-free" ringer's solution (0 ca2+/20 mm mg2+). glutamate also stimulated calcium-independent release, using concentrations as low as 100 microm. in contrast, release stimulated by 25 mm potassium was reduced by 80% in calcium- ... | 1990 | 1980204 |
| a slow and a fast secretory compartment of pomc-derived peptides in the neurointermediate lobe of the amphibian xenopus laevis. | 1. peptide release from the neurointermediate lobe of xenopus laevis has been studied using dual pulse-chase incubation, superfusion and hplc techniques. 2. lobes release pulse-labelled material in two phases, the first phase lasting about 6 hr, the second persisting up to 14 hr. 3. in both phases similar, pomc-derived peptides are released. their release can be inhibited by dopamine. 4. when release during the first phase is inhibited, newly synthesized peptides are shunted into the second rele ... | 1990 | 1980877 |
| the xenopus laevis hox 2.1 homeodomain protein is expressed in a narrow band of the hindbrain. | the expression pattern of the xenopus homeodomain protein hox 2.1 during development was determined using an affinity-purified antibody directed against a carboxyterminal peptide. nuclear staining was detected in a very narrow band of the hindbrain. this pattern was compared to that of the previously described xenopus gene xihbox 1 in serial sections and found to be more anterior than the xihbox 1 long protein expression but overlapping with that of the short protein. xenopus hox 2.1 protein exp ... | 1990 | 1981142 |
| movements of the large intestine in the anuran larvae, xenopus laevis. | 1. the contractile behavior of the large intestine of xenopus laevis tadpoles was studied. 2. the large intestine is divided into a colon and rectum, and shows three types of movements: rhythmic ascending (antiperistaltic) waves of contraction originating at the anal end of the large bowel, rhythmic longitudinal contractions in the rectum and colon, and irregular contractions. the first two patterns occur in the large bowel in situ and thus appear mature. the last one occurred only in older prep ... | 1990 | 1981343 |
| analysis of the mechanism of isoniazid-induced developmental toxicity with frog embryo teratogenesis assay: xenopus (fetax). | the developmental toxicity of isoniazid (inh) and the metabolites acetylhydrazide (ah) and isonicotinic acid (ina) were examined with the frog embryo teratogenesis assay-xenopus (fetax). late xenopus laevis blastulae were exposed to inh, ah, and ina for 96 h in two separate static-renewal tests with and without the presence of three differently induced metabolic activation systems (mas). the mas consisted of uninduced, aroclor 1254-induced, and inh-induced rat liver microsomes. addition of the i ... | 1990 | 1982910 |
| differential compartmentalization of plasmid dna microinjected into xenopus laevis embryos relates to replication efficiency. | circular plasmid dna molecules and linear concatemers formed from the same plasmid exhibit strikingly different fates following microinjection into xenopus laevis embryos. in this report, we prove quantitatively that only a minority of small, circular dna molecules were replicated (mean = 14%) from fertilization through the blastula stage of development. at all concentrations tested, very few molecules (approximately 1%) underwent more than one round of dna synthesis within these multiple cell c ... | 1991 | 1986227 |
| the xenopus b1 factor is closely related to the mammalian activator usf and is implicated in the developmental regulation of tfiiia gene expression. | the xenopus laevis tfiiia promoter contains a motif that has been implicated in promoter activation in late-stage oocytes and contains the sequence (-269) cacgtg (-264). a cdna encoding a protein (b1) that binds to this element has been cloned from x. laevis and xenopus borealis ovarian cdna libraries. we show that this protein is a member of the helix-loop-helix family of regulatory proteins and contains 80% sequence identity with the human adenovirus major late transcription factor (mltf or us ... | 1991 | 1986236 |
| 42sp48 in previtellogenic xenopus oocytes is structurally homologous to ef-1 alpha and may be a stage-specific elongation factor. | we have isolated the cdna for 42sp48 and ef-1 alpha from mixed stage oocytes and tailbud (stage 22) xenopus laevis cdna libraries by use of the cdna for human elongation factor-1 alpha (ef-1 alpha) as probe. the nucleotide and deduced amino acid sequences of the entire coding region of 42sp48 and ef-1 alpha cdna were established. the proposed functional homology of the proteins is reflected in highly conserved amino acid sequences (91% identity), while the large number of silent mutations at the ... | 1991 | 1988459 |
| structural analysis of the peptidyl transferase region in ribosomal rna of the eukaryote xenopus laevis. | accessible single-strand bases in xenopus laevis 28 s ribosomal rna (rrna) domain v, the peptidyl transferase region, were determined by chemical modification with dimethylsulfate, 1-cyclohexyl-3-(2-morpholinoethyl-carbodiimide metho-p-toluene sulfonate and kethoxal, followed by primer extension. the relative accessibilities of three rrna substrates were compared: deproteinized 28 s rrna under non-denaturing conditions (free 28 s rrna), 60 s subunits and 80 s ribosomes. overall, our experimental ... | 1991 | 1988683 |
| isolation of an active gene and of two pseudogenes for mouse u7 small nuclear rna. | three u7 rna-related sequences were isolated from mouse genomic dna libraries. only one of the sequences completely matches the published mouse u7 rna sequence, whereas the other two apparently represent pseudogenes. the matching sequence represents a functional gene, as it is expressed after microinjection into xenopus laevis oocytes. sequence variations of the conserved cis-acting 5' and 3' elements of u rna genes may partly explain the low abundance of u7 rna. | 1991 | 1989694 |
| [125i]bolton-hunter neuropeptide-y-binding sites on folliculo-stellate cells of the pars intermedia of xenopus laevis: a combined autoradiographic and immunocytochemical study. | it has previously been established that neuropeptide-y (npy) is a potent inhibitor of alpha msh release from the pars intermedia of the amphibian xenopus laevis. the location of binding sites for npy in the pars intermedia of the pituitary has now been studied with light microscopic autoradiography, using a dispersed cell labeling method with the specific npy receptor ligand [125i]bolton-hunter npy. the majority of radioactive labeling was associated with folliculo-stellate cells; the percentage ... | 1991 | 1989860 |
| the vacuolar protein-targeting signal of yeast carboxypeptidase is functional in oocytes from xenopus laevis. | carboxypeptidase y, a yeast vacuolar glycoprotein was expressed in oocytes from xenopus laevis and its biosynthesis and sorting were examined. in yeast, targeting to the vacuole, the functional equivalent of the lysosome, is not mannose-6-phosphate-receptor dependent. it was found that carboxypeptidase enters the secretory pathway of the oocyte and is there glycosylated, phosphorylated in the carbohydrate part and delivered to the lysosome. deletion of an amino acid sequence, previously shown to ... | 1991 | 1991465 |
| purification of a cysteine endopeptidase which is secreted with bioactive peptides from the epidermal glands of xenopus laevis. | the purification is reported of an endopeptidase, xscep1 (xenopus skin cysteine endopeptidase), present in skin secretions of xenopus. the procedure involved an initial concentration of the enzyme by batchwise anion-exchange chromatography and ammonium sulphate precipitation. the proteolytic activity, determined with z-phe-arg-amc (z, benzyloxycarbonyl; amc, 7-amidomethylcoumarin) as substrate, was fractionated by gradient ion-exchange chromatography, yielding a major component which was purifie ... | 1991 | 1991477 |
| isolation of cdnas partially encoding four xenopus wnt-1/int-1-related proteins and characterization of their transient expression during embryonic development. | to begin to study the functions of the wnt-1/int-1 gene family during vertebrate development, we have isolated four xenopus laevis cdnas encoding the partial sequence of proteins homologous to wnt-1/int-1. xwnt-3, xwnt-4, xwnt-5a, and xwnt-8 demonstrate between 35 and 50% amino acid identity with x. laevis wnt-1/int-1 and most cysteine residues are conserved. xwnt-4 and xwnt-3 transcripts are detected only during the neurula through tadpole stages of development. expression of xwnt-8 is observab ... | 1991 | 1991549 |
| organization, nucleation, and acetylation of microtubules in xenopus laevis oocytes: a study by confocal immunofluorescence microscopy. | anti-tubulin immunofluorescence and laser-scanning confocal microscopy were used to examine microtubule organization during xenopus oogenesis (dumont stages i-vi). stage i oocytes contained a poorly ordered microtubule array, characterized by concentrations of microtubule in the cortex, surrounding the germinal vesicle, and associated with the mitochondrial mass. no focus of microtubule organization was detectable by optical sectioning or in microtubule regrowth experiments, suggesting that stag ... | 1991 | 1991557 |
| biosynthesis and secretion of rat salivary proteins by xenopus laevis oocytes. | xenopus laevis oocytes injected with poly (a+) rna isolated from rat parotid and submandibular glands synthesize and secrete salivary proteins. amylase was identified in the media of cultured oocytes injected with rat parotid mrna by size and immunoprecipitation with anti-human amylase serum. secretion of the salivary proteins was detectable in the medium eight h following the parotid mrna injection and continued in a time-dependent fashion for up to 96 h. in contrast to rat parotid slices in cu ... | 1991 | 1991875 |
| the estrogen-regulated destabilization of xenopus albumin mrna is independent of translation. | protein synthesis inhibitors have been shown to increase the stability of a number of labile mrnas. in xenopus laevis serum albumin mrna is destabilized in the liver cell cytoplasm following estrogen administration. the present study examined the effect of translation inhibitors on this process. the initiation inhibitor 2-(4-methyl-2,6-dinitroanilino)-n-methylpropionamide causes accumulation of albumin mrna in 20-80s mrnp particles whereas the elongation inhibitor cycloheximide causes albumin mr ... | 1991 | 1993075 |
| rna-protein interactions of stored 5s rna with tfiiia and ribosomal protein l5 during xenopus oogenesis. | we studied the pathway of 5s rna during oogenesis in xenopus laevis from its storage in the cytoplasm to accumulation in the nucleus, the sequence requirements for the 5s rna to follow that pathway, and the 5s rna-protein interactions that occur during the mobilization of stored 5s rna for assembly into ribosomes. in situ hybridization to sections of oocytes indicates that 5s rna first becomes associated with the amplified nucleoli during vitellogenesis when the nucleoli are activity synthesizin ... | 1991 | 1995392 |
| cytological and biochemical analyses of the maternal-effect mutant embryos with abnormal cleavage furrow formation in xenopus laevis. | we describe an embryonic lethal mutation in xenopus laevis that provokes regression of cleavage furrow formation. the mutant females (designated as af) were obtained by the back-cross of a female with one of her sons. all the fertilized eggs laid by the mutant females, regardless of the wild-type male used in the mating, failed to cleave although each furrow ran at a proper position superficially. light and electron microscopic observations of the embryos revealed that the cleavage furrows staye ... | 1991 | 1995393 |
| novel angiotensin ii antagonists distinguish amphibian from mammalian angiotensin ii receptors expressed in xenopus laevis oocytes. | angiotensin ii (aii) stimulates rapid increases in cytosolic ca2+ concentrations in xenopus laevis oocytes after binding to specific receptors located in the surrounding follicular cells. in follicular oocytes, the peptide aii receptor antagonists saralasin (ic50 = 25 nm) and cgp 42112a (ic50 = 400 nm) were orders of magnitude more potent than the non-peptide antagonists dup 753 and pd-123177 (ic50 greater than 10 microm) as inhibitors of aii-induced ca2+ mobilization. the relative potencies of ... | 1991 | 1996080 |
| the xenopus localized messenger rna an3 may encode an atp-dependent rna helicase. | the maternal messenger rna an3 was originally identified localized to the animal hemisphere of xenopus laevis oocytes, eggs and early embryos. xenopus embryos depend on mrna and protein present in the egg before fertilization (maternal molecules) to provide the information needed for early development. localization of maternal mrna gives cells derived from different regions of the egg distinctive capacities for protein synthesis. we show here that an3 mrna encodes a protein with 74% identity to ... | 1991 | 1996140 |
| secondary structure of the 5' external transcribed spacer of vertebrate pre-rrna. presence of phylogenetically conserved features. | eucaryotic pre-rrna spacers are evolutionarily highly variable in sequence and size, and are markedly expanded in vertebrates, particularly in mammals. the longest mammalian spacer by far is the 3.5-4-kb 5' external transcribed spacer (5'-ets), which is excised in two steps. we present a folding model for the entire mammalian 5'-ets, derived from comparative analyses and thermodynamic predictions for mouse, rat and human sequences, which should prove helpful in identifying cis-acting processing ... | 1991 | 1999184 |
| purification of a 92-kda cytoplasmic protein tightly associated with the cell-cell adhesion molecule e-cadherin (uvomorulin). characterization and extractability of the protein complex from the cell cytostructure. | the transmembrane epithelial cell-cell adhesion protein e-cadherin (uvomorulin) associates via its cytoplasmic domain with three or more proteins whose structure and function are not yet established. the associated proteins, also termed catenins (ozawa, m., baribault, h., and kemler, r. (1989) embo j. 8, 1711-1717), are of interest because they may form a link to the cytoskeleton, and/or regulate e-cadherin function. in this report immunoprecipitates of e-cadherin complexes, isolated from xenopu ... | 1991 | 1999432 |
| poleward microtubule flux mitotic spindles assembled in vitro. | in the preceding paper we described pathways of mitotic spindle assembly in cell-free extracts prepared from eggs of xenopus laevis. here we demonstrate the poleward flux of microtubules in spindles assembled in vitro, using a photoactivatable fluorescein covalently coupled to tubulin and multi-channel fluorescence videomicroscopy. after local photoactivation of fluorescence by uv microbeam, we observed poleward movement of fluorescein-marked microtubules at a rate of 3 microns/min, similar to r ... | 1991 | 1999464 |
| mutations in 5s dna and 5s rna have different effects on the binding of xenopus transcription factor iiia. | the effects on tfiiia binding affinity of a series of substitution mutations in the xenopus laevis oocyte 5s rna gene were quantified. these data indicate that tfiiia binds specifically to 5s dna by forming sequence-specific contacts with three discrete sites located within the classical a and c boxes and the intermediate element of the internal control region. substitution of the nucleotide sequence at any of the three sites significantly reduces tfiiia binding affinity, with a 100-fold reducti ... | 1991 | 2001375 |
| transcription of the xenopus laevis selenocysteine trna(ser)sec gene: a system that combines an internal b box and upstream elements also found in u6 snrna genes. | the transcription mode of the xenopus trna(ser)sec gene by rna polymerase iii was deciphered by injection of mutant templates into xenopus oocyte nuclei. trna(ser)sec represents the paradigm of a new class of rna polymerase iii genes combining trna and u snrna gene regulatory elements. its promoter is tripartite, constituted by two upstream elements, a pse and a tata motif that are interchangeable with those of u6 snrna genes and an internal box b as in other trnas. the b box enables the transcr ... | 1991 | 2001675 |
| studies on the in vitro spermicidal activity of synthetic magainins. | two synthetic magainins a and g are shown to have spermicidal activity. transmission electron microscopic micrographs show that both magainins alter the plasma membranes of sperm and that these actions are rapid. further studies will better delineate the contraceptive potential of synthetic magainins. | 1991 | 2001767 |
| involvement of "hinge" nucleotides of xenopus laevis 5 s rrna in the rna structural organization and in the binding of transcription factor tfiiia. | nucleotides in the bifurcation region of the 5 s rrna, the junction of the three helical domains, play a central role in determining the coaxial stacking interactions and tertiary structure of the rna. we have used site-directed mutagenesis of xenopus laevis oocyte 5 s rrna to make all possible nucleotide substitutions at three positions in loop a (10, 11 and 13) and at the g66.u109 base-pair at the beginning of helix v. certain double point mutations were constructed to ascertain the relationsh ... | 1991 | 2002508 |
| micronuclei and chromosome aberrations in xenopus laevis spermatocytes and spermatids exposed to adriamycin and colcemid. | cultured testes and spermatocytes from the frog xenopus laevis have been incubated (40-42 h) with adriamycin or colcemid followed by quantitation of chromosome aberrations in secondary spermatocytes and quantitation of micronuclei in secondary spermatocytes, early round spermatids, and round spermatids with acrosomal vacuoles (av) at 18-162 h of culture. micronucleus frequencies were consistently higher in secondary spermatocytes relative to round spermatids after exposure to either adriamycin o ... | 1991 | 2002802 |
| direct measurement of intracellular pressure. | the feasibility of using the servo-null technique for direct measurement of intracellular pressure (pin) was investigated. a large cell, the xenopus laevis oocyte, was chosen for study, and it was established that pin obtained with this method was both stable and accurate in these cells. median resting pin in oocytes was found to be 0.27 cmh2o, range 0.14-0.61 cmh2o. during osmotic swelling pin increased, in a non-linear fashion, to a value of 4.11 cmh2o, range 2.61-8.91 cmh2o, with increases in ... | 1991 | 2003586 |
| cell cycle tyrosine phosphorylation of p34cdc2 and a microtubule-associated protein kinase homolog in xenopus oocytes and eggs. | we have examined the time course of protein tyrosine phosphorylation in the meiotic cell cycles of xenopus laevis oocytes and the mitotic cell cycles of xenopus eggs. we have identified two proteins that undergo marked changes in tyrosine phosphorylation during these processes: a 42-kda protein related to mitogen-activated protein kinase or microtubule-associated protein-2 kinase (map kinase) and a 34-kda protein identical or related to p34cdc2. p42 undergoes an abrupt increase in its tyrosine p ... | 1991 | 2005892 |
| cortical membrane-trafficking during the meiotic resumption of xenopus laevis oocytes. | changes in the organization of membranous structures in the amphibian oocyte cortex were studied during the process of progesterone-induced meiotic resumption. progesterone treatment of xenopus laevis oocytes induced short term and longer term changes in the cortical membranes. in the short term, progesterone induced a burst of endocytosis mediated through coated pits and coated vesicles. immuno-electron-microscopic localization of progesterone suggested that the progesterone receptor, bound to ... | 1991 | 2007258 |