Publications

isolation and structural analysis of ribosomal protein genes in xenopus laevis. homology between sequences present in the gene and in several different messenger rnas.		1982	6296397
characterization of histone genes isolated from xenopus laevis and xenopus tropicalis genomic libraries.	using a cdna clone for the histone h3 we have isolated, from two genomic libraries of xenopus laevis and xenopus tropicalis, clones containing four different histone gene clusters. the structural organization of x. laevis histone genes has been determined by restriction mapping, southern blot hybridization and translation of the mrnas which hybridize to the various restriction fragments. the arrangement of the histone genes in x. tropicalis has been determined by southern analysis using x. laevi ...	1982	6296782
organization and expression of cloned histone gene clusters from xenopus laevis and x. borealis.	we have isolated several clones containing xenopus histone genes from genomic libraries of x. laevis and x. borealis dna. each genomic clone has been mapped and the positions of 26 histone genes in seven laevis clones and 5 histone genes in one borealis clone have been determined. in laevis, the histone gene clusters show considerable variation in gene order within a single individual. when the cloned dnas were microinjected into the nucleus of xenopus oocytes, expression of cloned genes at the ...	1982	6296783
cyclic amp-mediated control of meiosis: effects of progesterone, cholera toxin, and membrane-active drugs in xenopus laevis oocytes.	progesterone depressed rapidly (50% at 1 min) and persistently cyclic amp (camp) concentration that had been elevated by cholera toxin in xenopus laevis oocytes. camp remained below 1 pmol per oocyte (mean basal level) for approximately 1 hr and thereafter rose to approximately 120% of control values, while germinal vesicle (nucleus) breakdown did not occur. in the absence of cholera toxin, progesterone treatment for 6 hr maintained camp concentration below the basal level (but not lower than 80 ...	1982	6278498
effects of n-methyl-n-nitrosourea on carrier-primed anti-hapten responses in xenopus laevis.	young adult xenopus laevis were treated with n-methyl-n-nitrosourea at doses which temporarily or permanently remove the thymic cortex and suppress allograft immune competence. their ability to mount a carrier-primed, helper t cell-mediated, hapten-specific response was tested in terms of numbers of antigen binding cells in the spleen. animals which had retained skin allografts for more than 300 days lacked helper activity, while those which had eventually rejected their allografts were able to ...	1982	6215271
[detection of collagen by immunofluorescence during development of xenopus (xenopus laevis daud.)].	appearance of the different collagen types was studied during the clawed toad development from hatching to metamorphosis, using indirect immunofluorescence techniques. type-like iv collagen of basement membranes was first seen in the notochord streath. type i, type ii were detected at the same time, followed by type iii. developmental sequence and distribution of the four collagen types indicate the different stages of organogenesis.	1982	6217869
na,k-atpase from xenopus laevis kidney and epidermis: ouabain interaction studies.	a satisfactory purification from xenopus laevis epidermis is presented. ki and kd values for the ouabain-enzyme interaction have been evaluated. both parameters appear very low, as compared with those demonstrated in other anurans. very low digitalis-like compound level was demonstrated in xenopus; on the contrary in bufo, in which these substances play a defensive role, it is very high. our results strengthen the hypothesis of a physiological action of such compounds in regulating enzyme-driven ...	1982	6299312
an amber suppressor trna gene derived by site-specific mutagenesis: cloning and function in mammalian cells.	we describe the synthesis, cloning, expression, and in vivo function of a suppressor trna gene in mammalian cells. by using "primer-directed mutagenesis" on a xenopus laevis tyrosine trna gene cloned into the recombinant single-strand phage m13mp5, we have generated an amber suppressor trna gene that has a nucleotide change--gta leads to cta--in the anticodon sequence. the suppressor (su) trna gene was introduced into monkey kidney cells (cv-1) by using simian virus 40 (sv40) dna as vector (sv40 ...	1982	6310546
comparative analysis of xenopus tropicalis and xenopus laevis vitellogenin gene sequences.	analysis of cdna clones synthesized from vitellogenin mrna of x. tropicalis revealed three different types of cdna clones, i.e. a, a* and b. a and a* clones have a sequence divergence of about 6% and are both related to x. laevis vitellogenin cdnas of subgroup a1 as well as a2 with a sequence divergence of 6-9%. b clones however, are related to x. laevis cdna clones of subgroup b1 and b2 with a sequence divergence of about 7%. while the a and b clones correspond to vitellogenin mrnas of similar ...	1982	6280148
characterization of the soluble cyclic nucleotide phosphodiesterases in xenopus laevis oocytes. evidence for a calmodulin-dependent enzyme.	cyclic nucleotide phosphodiesterase activities (3',5'-cyclic nucleotide 5'-nucleotidohydrolase, ec 3.1.4.17) were found in the 40,000 x g supernatant fraction of homogenates of xenopus laevis oocytes. in the supernatant, the ratio of the specific activity of cyclic amp phosphodiesterase to that of cyclic gmp phosphodiesterase was 1.1 at the 1 micro substrate level. two phosphodiesterase forms were isolated by centrifugation on sucrose gradient: a 3-4 s form hydrolyzing specificity cyclic amp and ...	1982	6280770
calcium requirement for alpha-msh action on tail-fin melanophores of xenopus tadpoles.	the role of ca2+ in alpha-msh action on melanophores was studied, in vitro, with a bioassay on ventral tail-fin pieces from tadpoles of xenopus laevis. melanosome dispersion induced by alpha-msh required 1-2 mm extracellular ca2+. gradual lowering of the extracellular ca2+ levels produced a concentration-dependent inhibition of the alpha-msh response; complete inhibition was obtained in a ca2+-free medium containing 10-4 m egta. in mg2+-free medium, normal dispersion was observed. the ca2+ antag ...	1982	6281099
temperature dependence of the sodium channel gating kinetics in the node of ranvier.	temperature dependence of the na+ channel gating kinetics was measured from the ionic and charge displacement currents in the node of ranvier of xenopus laevis, m3h kinetics was applied, assuming a delay, delta t, in the activation process. the rate constants for the m- and h-process showed arrhenius temperature-dependence with q10 of 2.34 and 2.9 respectively, while delta t exhibited non-arrhenius temperature-dependence. q10 for pna, measured as 1.6, was smaller than for the rate constants and ...	1982	6281846
quantitation of estrogen effect on xenopus laevis albumin mrna levels by hybridization to cloned albumin cdna.	the isolation and characterization of a xenopus laevis albumin cdna clone, pun18, is described. this clone was identified as a x. laevis albumin cdna clone by hybridization-mrna selection-translation and by other techniques. the clone was used in hybridizations to determine the effect of estrogen on albumin synthesis in livers of male x. laevis. we find that albumin mrna levels remain relatively constant during the massive induction of vitellogenin mrna synthesis and vitellogenin secretion which ...	1982	6282883
benzo(a)pyrene-binding proteins of hamster embryo cell nuclei: comparison of nuclear isolation procedures.	hamster embryo cells metabolize benzo(a)pyrene to derivatives that covalently modify the nuclear macromolecules including proteins. not all proteins are modified to the same extent nor by the same metabolites. in particular, a protein of apparent molecular weight 32,000 is highly modified by derivatives of trans-9,10-dihydro-9,10-dihydroxy b(a)p. this protein is shown here to be preferentially lost from nuclei during purification by centrifugation through high molarity sucrose solutions followed ...	1982	6282910
nucleotide sequence of an external transcribed spacer in xenopus laevis rdna: sequences flanking the 5' and 3' ends of 18s rrna are non-complementary.	we have sequenced the external transcribed spacer (ets) of a ribosomal transcription unit from xenopus laevis, together with sections of the preceding non-transcribed spacer. our analysis was carried out on the same cloned transcription unit as that from which the internal transcribed spacers (its) were previously sequenced. the ets is approximately 712 nucleotides long and, like the its regions, is generally very rich in c plus g. features of the sequence include an excess of oligo-c tracts ove ...	1982	6283480
lipid environments in the yolk lipoprotein system. a spin-labeling study of the lipovitellin/phosvitin complex from xenopus laevis.	lipid/protein and lipid/lipid interactions in the yolk lipoprotein complex from xenopus laevis were examined by introducing a series of lipid spin-labels into the complex and observing the electron spin resonance spectra as a function of the position of the label along the lipid chains, temperature, ph, and charge on the lipid polar head group. analyses of the spectra show that, in addition to the expected component arising from lipid associated with protein, a second component with increased se ...	1982	6284201
the dnase i sensitivity of xenopus laevis genes transcribed by rna polymerase iii.	since the initial discovery that the dnase i sensitivity of the globin genes in different cell types correlates with globin gene expression, this relationship has been shown to hold true for a variety of genes, including the genes for ovalbumin, conalbumun, alpha- and beta-globin in chicken, several heat-shock proteins in drosophila, the r-chromatin of tetrahymena and the viral polyoma minichromosome. although genes transcribed by rna polymerases i and ii have been studied extensively, the genes ...	1982	6285200
isolation and characterisation of the xenopus laevis albumin genes: loss of 74k albumin gene sequences by library amplification.	the blood of the frog x.laevis contains 2 albumins of 68,000 and 74,000 daltons which are encoded in the liver by two related mrnas. when an amplified x.laevis dna library was screened with cloned albumin cdna only 68,000 dalton albumin gene sequences were isolated. hybridisation of the albumin cdna to southern-blots of eco r1 digested x.laevis dna showed that the sequences present in the recombinants did not account for all the fragments which hybridised on the southern-blots. this indicated th ...	1982	6285309
sodium channels induced by depolarization of the xenopus laevis oocyte.	an electrically gated na+ channel can be made to appear in the membrane of the xenopus laevis oocyte by simple depolarization. this membrane normally responds passively to imposed transmembrane currents with resting potentials around -60 mv, but when it is held depolarized to more than about +30 mv it becomes possible to obtain long-lasting regenerative depolarizations up to +80 mv; these depolarizations can last as long as 20 min. this potential is due to an "induction" of a na+-dependent chann ...	1982	6285341
inheritance of dna methylation in microinjected eggs of xenopus laevis.	plasmid dna methylated at hpa ii sites was injected into eggs of xenopus laevis. the methylated dna replicates extrachromosomally, and the methylated state of the h pa ii sites is inherited through replication. unmethylated sites remain unmethylated in progeny molecules. to test whether replication is necessary for new methylation to occur, dna methylated on one strand only was injected and unreplicated dna was selected for analysis. methylation was copied onto a previously unmethylated strand i ...	1982	6285378
molecular cloning and characterization of ribosomal rna genes from the brine shrimp.	a library of genomic dna from the brine shrimp, artemia, has been constructed with the charon 4a phage vector, utilizing ecori passenger fragments. screening this library with purified xenopus laevis cloned rdna genes has resulted in the identification and plaque purification of a recombinant containing a complete artemia (18 s + 26 s) rdna repeat unit. a physical map derived from the analysis of restriction endonuclease digests of the repeat unit, which measures 13.9 kilobase pairs, is similar ...	1982	6285976
dnaase i sensitivity and methylation of active versus inactive rrna genes in xenopus species hybrids.	we studied the chromatin structure and methylation of ribosomal rna genes (rdna) in hybrids between xenopus laevis and xenopus borealis. s1-nuclease protection experiments showed that 97%-98% of the rrna precursor in hybrid tadpoles was of the x. laevis type. preferential expression of the laevis rdna was correlated with its hypersensitivity to dnaase i compared to borealis rdna. borealis and laevis rdnas gave equivalent methylation patterns, however. the results show that hypomethylated sites i ...	1982	6286140
membrane addition to rod photoreceptor outer segments: light stimulates membrane assembly in the absence of increased membrane biosynthesis.	the effect of light on the biosynthesis and the assembly of rod photoreceptor outer segment membranes was analyzed in vitro using retinas from xenopus laevis. the number of open discs at the base of the outer segment was used as a morphologic index to evaluate relative differences in rates of membrane assembly. assembly was stimulated in vitro by light, as evidenced by a greater number of open discs that accumulated in light-exposed retinas than that in retinas maintained under the same conditio ...	1982	6460718
an in vivo study of the ontogeny of alloreactivity in the frog, xenopus laevis.	pre- and perimetamorphic larval and post-metamorphic juvenile frogs (xenopus laevis) from a single family were grafted with skin from either of their patents (who differed from the hosts by one major histocompatibility complex (mhc) haplotype and multiple minor h loci) or from an unrelated adult (to provide a greater immunogenetic disparity). the fate of such skin grafts transplanted to hosts of various developmental stages indicated that a net destructive alloimmunity in this amphibian species ...	1982	6459993
the organization of the tadpole and adult alpha globin genes of xenopus laevis.	adult erythrocytes of x. laevis contain six electrophoretically resolvable globin polypeptides while tadpole erythrocytes contain four polypeptides, none of which comigrates with an adult protein. we show that three of the adult proteins are alpha globin polypeptides (alpha 1, alpha 2, alpha 3) and three are beta globin polypeptides (beta 1, beta 2, beta 3). we find that a tadpole alpha globin gene (alpha t1) is linked to the major adult locus in the sequence 5'-alpha t1-alpha 1-beta 1-3' with 5 ...	1982	6298702
the unmethylated state of the promoter/leader and 5'-regions of integrated adenovirus genes correlates with gene expression.	an inverse correlation has been established between the levels of dna methylation at 5'-ccgg-3' (mspi/hpaii) sites in specific genes of integrated viral dna in adenovirus type 12 (ad12)-transformed hamster cell lines and the extent to which these genes are expressed ( sutter and doerfler , 1979, 1980). in general, early genes are transcribed into mrna, while late genes are permanently switched off in these cell lines. adenovirus type 2 genes methylated in vitro at 5'-ccgg-3' sites are not transc ...	1982	6329677
18s coding sequences in amplified ribosomal dna from xenopus laevis oocytes are highly homogeneous, unmethylated, and lack major open reading frames.	we have used two approaches to search for sequence variants in the 18s coding region of amplified ribosomal dna (rdna) from xenopus laevis oocytes. first, using clones derived from amplified rdna, we compared the equivalent of a complete 18s coding region from two clones and short regions from two other clones with the 18s sequence previously determined from a "reference" clone. the respective sequences in all the clones were identical. secondly, we examined greater than 60% of the 18s sequence ...	1982	6329693
a prokaryotic trnatyr gene, inactive in xenopus laevis oocytes, is activated by recombination with an eukaryotic trnapro gene.	eukaryotic tdna promoters are composed of two essential regions contained within the coding sequence (box a and box b). due to the highly conserved structure of prokaryotic and eukaryotic trna, most prokaryotic trna genes are expected to be active templates in eukaryotic transcriptional systems. in this paper we show that escherichia coli tdnatyr is not transcribed in the nucleus of xenopus laevis oocytes. by in vitro construction of hybrid molecules between inactive prokaryotic tdnatyr from e. ...	1982	6329706
cloning and structure of the human immune interferon-gamma chromosomal gene.	two clones containing the human immune interferon-gamma (ifn-gamma) chromosomal gene were isolated from a human dna library present in lambda charon4a phage. dna from these clones specified biologically active interferon upon injection into the nuclei of xenopus laevis oocytes. analysis of the clones revealed that they were derived from the same chromosomal segment. restriction fragments that hybridized with 32p-labeled cdna probes were subcloned into plasmids and the complete sequence of the if ...	1982	6329718
the organization of ribosomal genes in vertebrates.	the organization of the repeat unit of the ribosomal genes has been determined in 15 different species of vertebrates. the ecori and bamhi restriction maps of the rdna from single individuals of different species of fishes, amphibians, and reptiles have been analysed. two rdna clones from xenopus laevis (representing one complete repeat unit) were used as probes in southern blots to detect restriction fragments containing ribosomal genes. the results obtained indicate that the transcribed region ...	1982	6329726
repetitive sequences associated with polyadenylated rna of xenopus laevis embryos.	electron microscopy revealed that transcripts of complementary repetitive sequence elements are widely distributed among long poly (a) containing rna molecules of xenopus laevis. cdna/rna hybridization experiments suggest that many of these polyadenylated transcripts carry protein coding sequences which are interrupted by repetitive elements. our in-vitro translation experiments indicate that removal of repetitive elements must precede the utilization of protein coding sequences associated with ...	1982	28305260
the fate of oocyte nuclear proteins during early development ofxenopus laevis.	the localization and movements of four nuclear proteins, originally contained in the germinal vesicle ofxenopus oocytes, were followed through early development from cleavage to late neurula. the study made use of monoclonal antibodies directed against germinal vesicle proteins. biochemical methods showed that all proteins persist in the embryo without a change in molecular size or gross concentration. at early stages the proteins are localized preferentially in the cytoplasm of the animal hemis ...	1982	28305052
the presence of an endogenous lectin in early embryos ofxenopus laevis.	xenopus laevis embryos were examined for the presence of endogenous carbohydrate binding proteins. soluble extracts of cleavage, gastrula and neurula embryos are able to agglutinate trypsinized rabbit erythrocytes. unlike other embryonic lectins this agglutination activity requires the presence of calcium ions but not of sulphydryl reducing agents. it is specifically inhibited by galactose and galactose containing derivatives. thiodigalactoside is the most potent disaccharide inhibitor followed ...	1982	28305386
synthesis of deuterium labeled cholesterol and steroids and their use for metabolic studies.	a simple method is described for the preparation of [6,7,7(-2)h3] sterols and steroids. the synthesis starts with a δ(5)-sterol or steroid and involves preparation of the 6-oxo-3α,5α-cyclosteroid, base exchange in the presence of deuterium oxide to introduce two deuteriums at the c-7 position and sodium borodeuteride reduction of the 6-oxo group to introduce the third deuterium atom at c-6. rearrangement of the [6,7,7(-2)h3]6α-hydroxy-3α,5α-cyclosteroid then gives the desired [6,7,7(-2)h3]-δ(5) ...	1982	27519440
in vitro synthesis and processing of wheat alpha-amylase : translation of gibberellic acid-induced wheat aleurone layer rna by wheat germ and xenopus laevis oocyte systems.	wheat (triticum aestivum) rna was used to program synthesis of the alpha-amylase protein by xenopus laevis oocytes. a 41,500-dalton protein was made which was identified as alpha-amylase by immunoprecipitation with rabbit anti-alpha-amylase antiserum raised against the purified wheat protein and by its co-migration with authentic alpha-amylase on sodium dodecyl sulfate polyacrylamide gels. synthesis of alpha-amylase was dependent upon injection of rna extracted from gibberellic acid-induced aleu ...	1982	16662149
turnip yellow mosaic virus rna is aminoacylated in vivo in chinese cabbage leaves.	turnip yellow mosaic virus (tymv) contains a trna-like structure as an integral part of its genome. this structure is located at the extreme 3' end of the viral rna and is the acceptor of valine after 3'-terminal adenylation. it is known that in vitro (with bacterial, yeast, or plant systems) and in vivo (upon microinjection into xenopus laevis oocytes) a series of trna-specific enzymes can recognize this structure in the viral rna. we report that tymv rna is valylated and consequently adenylate ...	1982	16453426
a prokaryotic trna gene, inactive in xenopus laevis oocytes, is activated by recombination with an eukaryotic trna gene.	[this corrects the article on p. 817 in vol. 1, pmid: 6329706.].	1982	16453433
the neuroanatomy of an amphibian embryo spinal cord.	horseradish peroxidase has been used to stain spinal cord neurons in late embryos of the clawed toad (xenopus laevis). it has shown clearly the soma, dendrites and axonal projections of spinal sensory, motor and interneurons. on the basis of light microscopy we describe nine differentiated spinal cord neuron classes. these include the rohon-beard cells and extramedullary cells which are both primary sensory neurons, one class of motoneurons that innervate the segmental myotomes, two classes of i ...	1982	17506218
intracellular recordings from spinal neurons during 'swimming' in paralysed amphibian embryos.	intracellular microelectrode recordings have been made from probable motoneurons in the spinal cord of xenopus laevis embryos during fictive 'swimming' in preparations paralysed with the neuromuscular blocking agent tubocurarine. these cells had resting potentials of -50 mv or more. during spontaneous or stimulus-evoked 'swimming' episodes: (a) the cells were tonically excited; the level of tonic synaptic excitation and the conductance increase underlying it were both inversely related to the 's ...	1982	17506219
experiments on the central pattern generator for swimming in amphibian embryos.	the central nervous system of paralysed xenopus laevis embryos can generate a motor output pattern suitable for swimming locomotion. by recording motor root activity in paralysed embryos with transected nervous systems we have shown that: (a) the spinal cord is capable of swimming pattern generation; (b) swimming pattern generator capability in the hindbrain and spinal cord is distributed; (c) caudal hindbrain is necessary for sustained swimming output after discrete stimulation. by recording si ...	1982	17506220
dna methylation patterns in the 5s dnas of xenopus laevis.	the frequency of cytosine methylation at specific sites in the somatic 5s dna (x1s) and trace oocyte 5s dna (x1t) of x. laevis has been determined using restriction enzymes that are inhibited by the presence of 5-methylcytosine (5mc) within their cleavage sequences. 5s dna methylation patterns were determined in genomic dna from mature red blood cells, which express neither type of 5s gene, and from liver, which expresses only x1s. all the sites examined in x1t are greater than 95% methylated in ...	1983	6298718
histone gene number and organisation in xenopus: xenopus borealis has a homogeneous major cluster.	using a xenopus laevis h4 cdna clone as a probe we have determined that the numbers of h4 histone genes in xenopus laevis and xenopus borealis are approximately the same. these numbers are dependent on the hybridization stringency and we measure about 90 h4 genes per haploid genome after a 60 degrees c wash in 3 x ssc. using histone probes from both xenopus and sea urchin we have studied the genomic organization of histone genes in these two species. in all of the x.borealis individuals analyzed ...	1983	6298735
characterization of the herpes simplex virus type 1 glycoprotein d mrna and expression of this protein in xenopus oocytes.	we have identified and characterized a 3.0 kilobase (kb) mrna containing coding sequences of the herpes simplex virus type 1 (hsv-1) glycoprotein d (gd) gene. the synthesis of this 3.0 kb mrna was unaffected by the presence of cytosine arabinoside, but was made in greatly reduced amounts in cells infected with hsv-1 in the presence of cycloheximide: it was, therefore, classified as an early mrna. by nuclease protection experiments, it was found that the 3.0 kb mrna is unspliced and, further, tha ...	1983	6298745
complete nucleotide sequence of a cloned cdna derived from the major adult alpha-globin mrna of x. laevis.	the complete sequence of a cloned cdna derived from the major adult alpha-globin mrna of xenopus laevis (the south african clawed toad) is presented. the sequence contains the complete coding and 3' non-coding regions of the mrna and part of the 5' non-coding region. the amino acid sequence of the encoded alpha-globin polypeptide has been deduced and is compared to other alpha-globin polypeptides. we find that the sequence is equally diverged from a bullfrog tadpole alpha-globin polypeptide and ...	1983	6298747
molecular cloning and sequencing of mrnas coding for minor adult globin polypeptides of xenopus laevis.	globin mrna was isolated from immature red blood cells of an adult xenopus laevis female. mrna/cdna hybrids were integrated in the pst i cleavage site of pbr 322 by g/c tailing, and cloned in escherichia coli strain hb 101. by restriction site analysis as well as hybridization behaviour we identified two clones coding for minor adult alpha and beta globin chains. nucleotide sequence analysis and derived amino acid sequences are presented.	1983	6298748
formation in vitro of sperm pronuclei and mitotic chromosomes induced by amphibian ooplasmic components.	a cell-free preparation of the cytoplasm from activated eggs of rana pipiens induces, in demembranated sperm nuclei of xenopus laevis, formation of a nuclear envelope, chromatin decondensation, initiation of dna synthesis, and chromosome condensation. both soluble and particulate cytoplasmic constituents are required to initiate these processes in vitro. the observed changes resemble processes occurring during fertilization and the mitotic cycle in early amphibian embryos. therefore, this cell-f ...	1983	6601299
comparative study of extracellular fibrils on the ectodermal layer in gastrulae of five amphibian species.	previous studies have shown the presence of a network of extracellular fibrils on the inner surface of the ectodermal layer of the ambystoma maculatum gastrulae. the alignment of the network along the blastopore-animal pole axis has suggested that the network of fibrils guides the migrating mesodermal cells in gastrulae by contact guidance. we have also shown that these fibrils can be deposited on substrata by explanted embryonic fragments and that substrata conditioned in this manner support di ...	1983	6602807
lipovitellin-phosvitin crystals with orthorhombic features: thin-section electron microscopy, gel electrophoresis, and microanalysis in teleost and amphibian yolk platelets and a comparison with other vertebrates.	yolk-platelet crystals in the teleosts pelvicachromis pulcher and noemacheilus barbatulus and the amphibians xenopus laevis, rana temporaria, r. esculenta, and triturus sp. have been studied by electron diffraction and imaging using a standardized processing (glutaraldehyde-osmium tetroxide fixation, glutaraldehyde-urea embedding, thin-section staining), by x-ray microanalysis, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis of their constituents. the crystal lattice is orthorhombi ...	1983	6602894
translation of human interleukin 2 mrna in xenopus laevis oocytes.	poly(a)-positive mrna extracted from tonsillar mononuclear cells stimulated with phytohemagglutinin-m and 12-o-tetradecanoyl phorbol 13-acetate was successfully translated into biologically active interleukin 2 (il-2) in xenopus laevis oocytes, and secreted into the incubation medium. in control experiments, the extract of oocytes injected with either poly(a)-negative rna or buffer did not show any il-2 activity. by sucrose density gradient centrifugation analysis, il-2 mrna was found as a singl ...	1983	6602934
cold- and heat-shock induction of new gene expression in cultured amphibian cells.	exposing primary epidermal cell cultures from the american bullfrog rana catesbeiana to elevated (greater than or equal to 32 degrees c; heat shock) or depressed (less than or equal to 5 degrees c; cold shock) temperatures for a short time results in the new and (or) enhanced synthesis of a 65 000 dalton (isoelectric point (pi) 6.7-6.9) polypeptide. with increasing temperature, a marked decrease in the synthesis of polypeptides observed at the control temperature (22 degrees c) and the new and ( ...	1983	6603891
the germinal vesicle material required for sperm pronuclear formation is located in the soluble fraction of egg cytoplasm.	the chromatin of xenopus laevis sperm nuclei was induced to decondense, swell and form mitotic chromosomes following its injection into mature rana pipiens oocytes. in contrast, the sperm chromatin did not decondense or form mitotic chromosomes when injected into oocytes from which the germinal vesicle (gv) was removed prior to the initiation of maturation. injection into enucleated oocytes of the material extracted from manually-isolated gvs restored their ability to decondense sperm nuclei. th ...	1983	6605256
dual contribution of embryonic ventral blood island and dorsal lateral plate mesoderm during ontogeny of hemopoietic cells in xenopus laevis.	the early embryonic development of hemopoietic cells in xenopus laevis was examined. either dorsal lateral plate (dlp) or ventral blood island (vbi) mesoderm was reciprocally transplanted between cytogenetically distinct (2n or 3n) stage 14 to 19 (neural fold) embryos. f-dna content of circulating erythrocytes was assayed at stages 40, 41, 43, 45, and 49. the f-dna content of cells in the thymus and mesonephros was assayed at stage 49. f-dna values were used to distinguish between donor or host ...	1983	6605382
mechanical, electrical, and morphological characteristics of skeletal muscle fibers from xenopus and other species of frogs.	mechanical, electrical, and morphological properties of iliofibularis or semitendinosus of xenopus laevis, rana catesbeiana, and rana nigromaculata were investigated in an attempt to find out the differences between them which will give the basic knowledge for the study of excitation-contraction coupling. with application of electrical stimulation, a single muscle fiber from xenopus contracted at a faster rate of rise than did the other muscles tested. the maximum rate of rise (tmax) of tension ...	1983	6606063
is caerulein amphibian cck?	the amphibian skin decapeptide caerulein is structurally related to the mammalian peptides gastrin and cck, suggesting that the peptides might share a common evolutionary history. it has been suggested that caerulein is the amphibian counterpart of gastrin and cck, and that the amphibia do not possess authentic gastric and cck. high performance liquid chromatography (hplc) in conjunction with radioimmunoassay using a caerulein-specific antiserum and c-terminal cck antisera, was used to character ...	1983	6606162
cytoplasmic phases in the first cell cycle of the activated frog egg.	the first cell cycle of the activated frog egg is longer than subsequent cycles and several developmentally important events such as the determination of bilateral symmetry occur at this time. when eggs of rana pipiens or xenopus laevis are dissected at times after activation, differences in the consistency of the animal half cytoplasm can be detected visually, and the first cell cycle has been divided into four cytoplasmic phases on this basis. phase 1 includes the events of activation and last ...	1983	6606589
transcription of a cloned xenopus laevis h4 histone gene in the homologous frog oocyte system depends on an evolutionary conserved sequence motif in the -50 region.	a cloned xenopus laevis h4 histone gene has been expressed in the x.laevis oocyte nucleus. the homologous histone h4 gene can be correctly and efficiently expressed in the frog oocyte even in presence of bacterial vector dna. as revealed by both analytical gel electrophoresis and s1 mapping, two h4 mrnas are specified with different transcriptional efficiencies from the tandemly repeated promoter. results from deletion mapping of the sequences essential for promoting h4 transcription show that d ...	1983	6324093
multiple forms of dna-dependent rna polymerases in xenopus laevis. rapid purification and structural and immunological properties.	dna-dependent rna polymerases i, ii, and iii (ec 2.7.7.6) were isolated from xenopus laevis ovaries. the soluble enzymes were precipitated with polyethyleneimine and subjected to chromatography on heparin-sepharose, deae-sephadex, and phosphocellulose. rna polymerase i was subjected to an additional chromatographic step on cm-sephadex. the procedure required 40 h and produced purified rna polymerase forms ia, iia, and iii in yields of 5 to 40%. the specific activities of rna polymerases iia and ...	1983	6401728
microinjection of purified ornithine decarboxylase into xenopus oocytes selectively stimulates ribosomal rna synthesis.	this study has utilized stage vi oocytes of xenopus laevis which have amplified the rdna gene 1,000-fold to assess whether the microinjection of ornithine decarboxylase (orndcase) would stimulate [alpha-32p]guanosine incorporation into 45s and 18s/28s rna selectively. the injection of purified orndcase into individual oocytes resulted in a greater than 2-fold increase in the incorporation of [32p]guanosine into 45s rna and 18s/28s rna with no increased incorporation into low molecular weight rna ...	1983	6402779
effects of diltiazem on skinned skeletal muscle fibers of the african clawed toad.	to examine the effects of diltiazem and its l-cis isomer (which possesses only a weak ca++-antagonistic action) on the contractile system and the sarcoplasmic reticulum of skeletal muscle, we used skinned fibers isolated from iliofibularis muscle of the african clawed toad, xenopus laevis. diltiazem showed the following effects: an increase in the ca++ sensitivity of the contractile system, a decrease in the maximal tension developed in a saturating concentration of ca++, an inhibition of ca++ u ...	1983	6403257
developmentally regulated rna binding proteins during oogenesis in xenopus laevis.	during oogenesis, xenopus oocytes synthesize and accumulate all types of rna. in particular, they store poly(a+) rna to such an extent that only about 5% is actually translated in the oocyte. using a protein blotting and in vitro binding assay, we have identified proteins which are associated with poly(a+) rna and perhaps other rnas as well. two groups of binding proteins were identified. the first group accumulates during oogenesis, generally is less than 50,000 molecular weight, and sediments ...	1983	6403538
melanophore differentiation in xenopus laevis, with special reference to dorsoventral pigment pattern formation.	during the development of xenopus laevis, after stage 26, a large number of dopa-positive cells were observed in the ventral region. electron microscopic observations revealed that these cells became localized in the epidermal layer and contained premelanosomes. in cultured ventral skin, fully matured melanophores appeared. these results strongly suggest that a large number of melanoblasts are present in the ventral epidermis and remain there without final differentiation into melanized melanoph ...	1983	6411851
[inhibitory effect of lectins extracted from arachis hypogea and soybeans on germ cell migration in the embryo of xenopus laevis (amphibia, anura)].	effect of injection of arachis hypogea (pna) and soybean (sba) lectins on the migration of xenopus primordial germ cells (pgcs) were investigated. pna inhibited almost entirely the pgcs migration, more than sba. our results indicated that the inhibition of the migration could be a consequence of the lectin-induced alterations of cell surface properties.	1983	6412978
characterization of trna precursor splicing in mammalian extracts.	transcription of a xenopus laevis trnatyr gene and splicing of the transcript have been studied in hela cell extracts. this trnatyr gene has a 13-base intervening sequence and is expressed as mature trna when transfected into mammalian cells. the trnatyr gene is transcribed under conditions of low concentrations of magnesium and atp, but is processed by splicing only when both of these cofactors are added at higher concentrations. the endonucleolytic activity of the trna-splicing system in the h ...	1983	6413507
5'-flanking sequences that inhibit in vitro transcription of a xenopus laevis trna gene.	two series of deletion mutants have been constructed in the 5'-flanking dna of a variant methionine trna gene of x. laevis. when assayed in homologous cell-free extracts, mutants of both series are expressed at very different levels and they initiate transcription at either or both of the two major sites used by the wild-type gene. no similarities are evident in the 5'-flanking regions of well expressed mutants, but two dna segments are identified that inhibit transcription. the most inhibitory ...	1983	6414719
analysis of the chromatin assembled in germinal vesicles of xenopus oocytes.	we have injected circular dna, labeled with 32p at a single restriction site, into germinal vesicles of xenopus laevis oocytes in order to study the nucleosome arrangement on the assembled minichromosomes. two types of genes were used in these studies, the somatic 5 s rna gene unit of xenopus borealis and the histone gene unit of drosophila melanogaster. we find that injections of labeled dna alone, at 1 ng dna per oocyte, results in irregularly spaced nucleosomes and partially supercoiled dna m ...	1983	6415291
[comparative effects of an extract of anguilla stannius corpuscles and of an active fragment of human parathyroid hormone (1-34 hpth) on an anuran batracian, xenopus laevis].	parathyrin of the corpuscles of stannius (pcs), glands which are restricted to holostei and teleostei, resembles mammalian parathyroid hormone secreted by the parathyroids. these glands made their first phylogenic appearance with amphibians, whereas the stannius corpuscles disappeared. we have compared, in the clawed toad, xenopus laevis, the effects of injections of extracts of corpuscles of stannius and of the active synthetic fragment of parathyrin (1-34 hpth). both hormones elicited hypocalc ...	1983	6416629
xenopus laevis lectin is localized at several sites in xenopus oocytes, eggs, and embryos.	the endogenous lectin of xenopus laevis oocytes, unfertilized eggs, and blastula-stage embryos was immunohistochemically localized using a highly specific antiserum. each tissue was examined with several techniques, including paraformaldehyde or glutaraldehyde fixation, frozen or plastic sections, and immunofluorescence or immunoperoxidase staining. in oocytes and unfertilized eggs, lectin was detected in association with yolk platelets, cortical granules, and the vitelline envelope. in embryos, ...	1983	6417146
the cytostatic effect of the cytoplasm of mature, non-activated and cleaving eggs of rana temporaria, acipenser stellatus and xenopus laevis.	corroborated here is the fact, earlier established by chulitskaya and felgengauer (1977), that the cytoplasm of mature non-activated eggs of rana temporaria and acipenser stellatus, unlike that of rana pipiens, exerts no cytostatic effect on the nuclei of the cleaving embryo, but acquires such a capacity after being treated with egta. egta treatment imparts cytostatic properties also to the cytoplasm of cleaving embryos. revealed is the dependence of the cytostatic effect and death of injected e ...	1983	6420076
corticotropin-releasing factor (crf)-like immunoreactivity in the vertebrate endocrine pancreas.	the light microscopic immunocytochemical localization of corticotropin-releasing factor (crf) is described in the endocrine pancreas of several species representing the major classes of vertebrates: fishes (channel catfish, ictalurus punctatus), amphibians (african clawed toad, xenopus laevis), reptiles (chameleon, anolis carolinensis), birds (chicken, gallus domesticus), and several mammals (rat, mouse, cat, rhesus monkey, and man). the crf-containing cells are scattered over the entire islet t ...	1983	6340106
ontogeny and characterization of mitogen-reactive lymphocytes in the thymus and spleen of the amphibian, xenopus laevis.	the ontogeny of the proliferative response of xenopus thymocytes to the t-cell mitogens concanavalin a (con a) and phytohaemagglutinin and to the b-cell mitogen e. coli lipopolysaccharide (lps) is examined during the first 2 years of life. responses after metamorphosis are compared with those occurring in the spleen. during much of larval life, mitogen-treated thymocytes display no sign of elevated [3h]tdr uptake. a low level in vitro response to con a and lps emerges transiently just prior to m ...	1983	6343233
maturation-promoting factor induces nuclear envelope breakdown in cycloheximide-arrested embryos of xenopus laevis.	we have studied the effect of maturation-promoting factor (mpf) on embryonic nuclei during the early cleavage stage of xenopus laevis development. when protein synthesis is inhibited by cycloheximide during this stage, the embryonic cell cycle arrests in an artificially produced g2 phase-like state, after completion of one additional round of dna synthesis. approximately 100 nuclei can be arrested in a common cytoplasm if cytokinesis is first inhibited by cytochalasin b. within 5 min after injec ...	1983	6345556
the thymus dependency of transplantation allotolerance in the metamorphosing frog xenopus laevis.	larval as well as adult frogs (xenopus laevis) are immunocompetent. yet, whereas adults will vigorously reject mhc-incompatible skin grafts, metamorphosing larvae may not. previous studies have revealed that this graft survival reflects an immunologically specific host tolerance. the role of the thymus in the acquisition of this tolerance to mhc-disparate skin allografts by metamorphosing outbred and inbred frogs has been investigated. when thymectomy was performed during midlarval or late larva ...	1983	6346599
response to skin grafts exchanged among siblings of larval and adult gynogenetic diploids in xenopus laevis.	gynogenetic diploid individuals were produced in an anuran amphibian, xenopus laevis, and their response to skin grafts exchanged among siblings was studied. all skin grafts exchanged among nongynogenetic sibling froglets, as well as those from genetically unrelated donors, were rejected within 30 days. more than half (57%) of the gynogens that received grafts from sibling partners exhibited a prolonged survival (over 30 days), including long-term survival of over 120 days in 13%. the skin graft ...	1983	6346617
specific in vivo and nonspecific in vitro alloreactivities of adult frogs (xenopus laevis) that were thymectomized during early larval life.	thymectomy of very young xenopus larvae abrogated in vitro proliferative responses to phytohemagglutinin (pha) and allogeneic leukocytes. thymectomized (txd) frogs, however, still rejected first-set skin allografts chronically and second-set grafts (but not third-party grafts) more rapidly. the specific second-set rejection reaction by txd frogs was transferable in vivo to secondary txd hosts (with major histocompatibility complex identical to the cell donor) by the subcutaneous injection of a m ...	1983	6347694
allograft rejection in xenopus laevis following larval thymectomy.	xenopus laevis thymectomized at stages 41 through 49 accept first set allografts, while animals thymectomized at stage 51 or older reject allografts in times similar to intact animals. however, thymectomy at progressively earlier stages results in a greater proportion of animals unable to reject second set grafts. in some animals, the allograft response remains deficient even after multiple challenges. the results indicate that alloreactive cells are thymus dependent, and suggest that the thymus ...	1983	6347739
isolation of chlamydia psittaci from naturally infected african clawed frogs (xenopus laevis).	an inclusion-forming agent was isolated from the livers of commercially raised african clawed frogs (xenopus laevis) involved in an epizootic of high morbidity and mortality. original isolation was made in mccoy cells. this agent was identified as chlamydia psittaci based on the formation of typical intracytoplasmic inclusions which developed within 48 h, were not stained by iodine, and were resistant to sulfadiazine. the isolate from one particular frog (designated as strain 178) was further st ...	1983	6347897
mitochondrial transfer rna genes from fungi (aspergillus nidulans) and plants (lupinus luteus) are transcribed in xenopus laevis oocyte nuclei.	three plasmids containing aspergillus nidulans mitochondrial transfer rna genes were microinjected into the nucleus of xenopus laevis oocytes. plasmids that contained a single trnacys gene or two trna genes (arg and asn) yielded trna-sized transcripts. plasmids containing cloned lupinus mitochondrial trna genes were also transcribed and processed in x. laevis nuclei.	1983	6350603
steroidal and peptidic control mechanisms in membrane of xenopus laevis oocytes resuming meiotic division.	stage 5-6 xenopus laevis oocytes are arrested in the prophase of the first meiotic division, and can be studied in vitro after removal from their follicle cell environment. while they do not mature spontaneously, they demonstrate germinal vesicle (nucleus) breakdown (gvbd) if exposed to approximately 1 microm progesterone, the hormone released in vivo at the time of ovulation and maturation. they become an egg ready to be fertilized. the progesterone-oocyte interaction, contrary to what is obser ...	1983	6350717
induction of germinal vesicle breakdown in xenopus laevis oocytes: response of denuded oocytes to progesterone and insulin.	denuded oocytes freed of their vitelline envelope have been prepared by two methods, enzymatically with pronase and manually by microdissection. the response of denuded oocytes to progesterone, in terms of germinal vesicle breakdown (gvbd), was similar to that obtained with defolliculated oocytes (separated with collagenase from follicle cells, but still keeping their vitelline membrane). the same conclusion was drawn with respect to morphological features of the oocyte surface observed by trans ...	1983	6352367
site-directed in vitro replacement of nucleosides in the anticodon loop of trna: application to the study of structural requirements for queuine insertase activity.	we have investigated the specificity of the enzymes q-insertase and mannosyl-q transferase that replace the guanosine at position 34 (wobble base) in the anticodon of several trnas by q or mannosyl-q derivatives. we have restructured in vitro the normal anticodon of yeast trna-asp-guc, yeast trnaargicg and yeast trnaleuuag. with yeast trna-asp-guc, we have replaced one or several nucleotides in the vicinity of g34 by one of the four canonical nucleotides or by pseudouridylic acid; we have also c ...	1983	6354708
development of the lateral line system in xenopus laevis. i. normal development and cell movement in the supraorbital system.	during development of xenopus laevis, the supraorbital lateral line system (i.e. the parietal and supraorbital lines of organs and the anterior auditory group of organs) is all derived from a single primordium located in the ear region of the epidermis. the primordium elongates first by active movement along the dorsal margin of the eye. individual primary organs are then formed by progressive fragmentation of the streak-like primordium. after fragmentation, passive displacement of the organs du ...	1983	6355359
[intercellular relay interactions in explants of amphibian embryonic tissues. i. intercellular relay interactions in normal explant morphogenesis].	in the explants of lateral mesoderm, together or without the overlaying ectoderm, taken from the neurula-early tail bud of amphibian embryos (xenopus laevis, rana temporaria) within 5-30 min, several types of cytological transformations have been observed, some of these being: formation of a microfilamentous layer under the naked explant surface, morphological polarization, and unilateral spreading of cells. these processes are described at the light and electron microscopy levels. it is suggest ...	1983	6356533
mitogenic responses of frog lymphocytes to crude and purified preparations of bacterial lipopolysaccharide (lps).	we have compared in vitro mitogenic responses of frog (xenopus laevis and rana pipiens) lymphocytes to various preparations of lipopolysaccharide (lps). commercial lps prepared from e. coli (phenol extraction) and from s. abortus-equi (phenol and tca extraction procedures) was mitogenic for frog lymphocytes. after reextraction of these lps preparations with phenol-water, the remaining lps was either considerably less mitogenic or not mitogenic. purified e. coli 055:b5 lps, prepared by phenol wat ...	1983	6357879
tolerance maintenance depends on persistence of the tolerizing antigen: evidence from transplantation studies on xenopus laevis.	in order to assess the role of antigen persistence in the tolerant state, tolerance was induced in xenopus laevis by the embryonic transplantation of whole eyes or tail tissue. both types of transplants were seen to heal in and persist, with no signs of immunological incompatibility. at metamorphosis, tail resorption occurred and grafted tail tissue was lost. eye transplants were maintained through metamorphosis in most eye grafted animals. eye graft recipients which had maintained the transplan ...	1983	6357880
the number of synaptic boutons terminating on xenopus cardiac ganglion cells is directly correlated with cell size.	the relationship between the size of parasympathetic neurones and the number of synaptic boutons terminating upon them has been studied in the cardiac ganglion of xenopus laevis. synaptic boutons were visualized by impregnation with zinc iodide and osmium (zio), which by electron microscopy was shown to stain heavily all synaptic boutons in six preparations. light microscopic examination of the unipolar ganglion cells in intact tissue reveals that larger neurones have more synaptic boutons. the ...	1983	6358464
detergent-soaked hrp-chips: a new method for precise and effective delivery of small quantities of the tracer to nervous tissue.	we dissolved horseradish peroxidase (hrp) in a 5% aqueous detergent solution (nonidet p-40) and dried it to a solid mass which was then fragmented into small chips of convenient size. these were applied to the cut or crushed oculomotor nerves of xenopus laevis tadpoles. this method combines the advantages of solid hrp (high concentration) and the presence of a detergent (enhanced uptake). moreover, as compared to chips of hrp alone, addition of the detergent facilitated the manipulation of the c ...	1983	6358709
sequence analysis of 28s ribosomal dna from the amphibian xenopus laevis.	we have determined the complete nucleotide sequence of xenopus laevis 28s rdna (4110 bp). in order to locate evolutionarily conserved regions within rdna, we compared the xenopus 28s sequence to homologous rdna sequences from yeast, physarum, and e. coli. numerous regions of sequence homology are dispersed throughout the entire length of rdna from all four organisms. these conserved regions have a higher a + t base composition than the remainder of the rdna. the xenopus 28s rdna has nine major a ...	1983	6359063
alcohol dehydrogenase isozymes in the clawed frog, xenopus laevis.	alcohol dehydrogenase (adh; ec 1.1.1.1) activity in xenopus laevis was highest in liver tissue, with decreasing activities in kidney, heart, and gut tissues, respectively. essentially no activity was found among other tissues screened, including lung, ovary, eye, and testes. also, there was no apparent sexual dimorphism of adh activity in either liver or kidney tissue. all adh isozymes were inhibited by 10 mm pyrazole, and no eye-specific retinol dehydrogenase activity was detected on starch gel ...	1983	6362654
mitochondrial dna-binding proteins that bind preferentially to supercoiled molecules containing the d-loop region of xenopus laevis mtdna.	from the bulk of the xenopus laevis mitochondrial proteins insoluble in 1% triton x-100 + 1m nacl, we have isolated, by dna-cellulose chromatography, a protein fraction enriched in dna-binding proteins. this fraction contains proteins showing a specific affinity for supercoiled dna molecules containing the mitochondrial dna displacement-loop region, as measured by filter binding and competition assays.	1983	6362668
stabilization of the maturation promoting factor (mpf) from xenopus laevis oocytes. protection against calcium ions.	maturation promoting factor (mpf) activity was recovered from progesterone-matured xenopus oocytes cytosol, fractionated by polyethylene glycol-20,000 or ethanolic precipitation. an improved stabilization of the biological activity was obtained by adding adenosine 5'-o-(3-thiotriphosphate) (atp-gamma-s) (50 microm) to the preparation buffers. neither ca2+ ions nor calmodulin inhibit the partially purified mpf.	1983	6362894
developmental change of a depolarization-induced sodium permeability in the oocyte of xenopus laevis.	in the full grown oocyte of xenopus laevis, a sodium permeability can be induced by depolarization to positive potential with current injection. voltage-clamp analysis has shown that depolarization causes a long-lasting modification of the membrane during which voltage-gated sodium channels become functional. in the present study, i have looked for the existence of these channels during cell growth. the channels appear during a very restricted period of cell growth, corresponding to dumont stage ...	1983	6311650
spontaneous release of transmitter from growth cones of embryonic neurones.	a nerve process grows by inserting new membrane material at its advancing tip, the growth cone. in embryonic cell culture and in embryos of xenopus laevis, many growth cones establish functional synaptic transmission within minutes after contact with muscle cells. the rapidity of synapse formation suggests that the growth cone may have already acquired the appropriate neurotransmitter and the machinery for transmitter release before encountering the target cell. here, we have used a patch of out ...	1983	6312327
the 1723 element: a long, homogeneous, highly repeated dna unit interspersed in the genome of xenopus laevis.	we describe a highly repeated dna element in the xenopus laevis genome. this sequence, named the 1723 element, was first identified among sequences that are transcribed during embryonic development. the element is present in about 8500 copies per haploid genome, which together accounts for about 2.4% of the genome. most copies of the element have highly conserved restriction maps, and are interspersed in the genome. the copies range in size from 6000 to 10,000 base-pairs due to an expandable reg ...	1983	6313946
satellite dna from xenopus laevis: comparative analysis of 745 and 1037 base pair hind iii tandem repeats.	highly repetitive hind iii restriction fragments of 0.72-0.76 kbp from total xenopus laevis genomic dna are organized in a tandem like arrangement. cloning of these fragments in pbr 322 with subsequent restriction site mapping and nucleotide sequence analysis of some selected clones showed two different types of sequences. 25-30% of material represent the oocyte specific 5 s dna repeat units, 70-75% are similar to the recently described repeat elements of satellite 1 dna. hybridization of a geno ...	1983	6314270
steroid and peptide control mechanisms in membrane of xenopus laevis oocytes resuming meiotic division.	stage 5-6 xenopus laevis oocytes are arrested in prophase of the first meiotic division, and can be studied in vitro after removal from their follicle cell environment. while they do not mature spontaneously, they demonstrate germinal vesicle (nucleus) breakdown (gvbd) if exposed to approximately 1 microm-progesterone (the hormone released in vivo at the time of ovulation and maturation). the oocytes' then become eggs ready to be fertilized. the progesterone-oocyte interaction, contrary to what ...	1983	6315317
the oocyte as an endocytic cell.	oocytes of xenopus laevis grow primarily by sequestering vitellogenin (vtg) selectively from the maternal bloodstream. morphological observations have demonstrated that an endocytic system is responsible for vtg uptake. binding studies indicate the presence of 2-28 x 10(10) surface vtg receptors per oocyte. these are continuously internalized into endosomes whether or not they are occupied by vtg, and other macromolecules may become trapped in the process. vtg-containing endosomes give rise to d ...	1983	6315318
herpes simplex virus defective genomes: structure of hsv-1 ang defective dna of class ii and encoded polypeptides.	sequence organization and origin of hsv-1 strain angelotti (ang) class ii defective dna (hsv-1 ang ddna1) were examined in detail by establishing physical maps and by molecular cloning. ddna1 consists of concatemers of tandem repeat units in which sequences from the ul region spanning map coordinates 0.37 to 0.415 of standard hsv ang dna are covalently linked to trs/irs sequences. the size of the repeat unit was determined to be about 8.9 kilobase pairs (kb), comprising sequences of 7.3 kb from ...	1983	6315866
a hyperpolarization-activated chloride current in xenopus laevis oocytes under voltage-clamp.	voltage-clamp experiments have been performed on ovulated xenopus laevis oocytes. two kinds of oocytes were studied: mature oocytes presenting the white spot due to germinal vesicle breakdown (gvbd) were found to be essentially unexcitable; oocytes without the white spot appeared to possess ionic channels which open transiently on hyperpolarization. the current is carried by chloride ions and, in holtfreter's solution, has a reversal potential at approximately - 15 mv.	1983	6316254
the structure of rat 28s ribosomal ribonucleic acid inferred from the sequence of nucleotides in a gene.	the nucleotide sequence of a rat 28s rrna gene was determined. the 28s rrna encoded in the gene contains 4718 nucleotides and the molecular weight estimated from the sequence is 1.53 x 10(6). the guanine and cytosine content is 67%. the sequence of rat 28s rrna diverges appreciably from that of saccharomyces carlsbergensis 26s rrna (about 50% identity), but more closely approximates that of xenopus laevis 28s rrna (about 75% identity). rat 28s rrna is larger than the analogous nucleic acids from ...	1983	6316273
[electrotonic transmission between primary afferent fibers and the motor neurons of the isolated spinal cord of various representative amphibians].	studies have been made of monosynaptic excitatory postsynaptic potentials elicited by stimulation of the posterior root in motoneurones of the isolated spinal cord of the frog rana ridibunda, toad bufo bufo, and clawed toad xenopus laevis. in all the amphibians studied, the early component of monosynaptic epsp was not blocked in ca-free medium containing 2 mm mn2+. it is suggested that electrical coupling in anuran amphibians reflects certain stage of evolution of the synaptic transmission in ve ...	1983	6316697