| characterization of na+/k+-atpase from xenopus laevis kidney. preliminary results. | in xenopus laevis, the renal na+/k+-dependent atpase is a very important enzyme involved in osmoregulatory processes and active transport. the enzyme was obtained from a microsome fraction purified by sucrose discontinuous gradient (10%, 15%, 29.4%) ultracentrifugation after sds treatment, and concentrated in the denser layer. the assayed biochemical parameters and their values are: 1) km (atp): 0.24 mm; 2) k1/2 (na+): 20.6 mm; 3) k1/2 (k+) 1.6 mm; 4) ki (ouabain): 0.025 micrometer; 5) optimum p ... | 1980 | 6261778 |
| replication of heterologous dna in xenopus laevis oocytes. | | 1981 | 6262120 |
| interaction between motor axons from two different nerves reinnervating the pectoral muscle of xenopus laevis. | 1. an electrophysiological and morphological study of sprouting and regeneration of motor nerves has been performed in the dually innervated pectoral muscle of xenopus laevis. 2. section of one of the nerves induced axon sprouting in the intact nerve. synapse formation by the sprouting axons was slow since the intact nerve took more than 3 months to increase its field of innervation by 70%. the rate of axon regeneration was faster than that of axon sprouting since the cut nerve reinnervated its ... | 1981 | 6262504 |
| nucleotide sequence of the initiation site for ribosomal rna transcription in drosophila melanogaster: comparison of genes with and without insertions. | the sequence of 470 nucleotides surrounding the initiation site for rrna transcription in drosophila melanogaster has been determined. the precise initiation site was determined first by measuring the dna fragment protected by the rrna precursor against digestion by the single-strand specific nuclease s1 and second by direct sequence determination of the first 13 nucleotides of the rrna precursor. because greater than 80% od rrna precursor molecules have been shown previously to bear pppa or ppa ... | 1981 | 6262809 |
| [meiotic maturation of the ovocyte of xenopus laevis : a 4-step mechanism]. | microinjection of the pure inhibitor (1) of camp dependent protein kinases (1.5 mum) into xenopus oocytes triggered 100% germinal vesicle break down (gvbd), faster than progesterone and slower than the maturation promoting factor (mpf). cholera toxin does not block (i) induced maturation; however cycloheximide inhibits (i) but not mpf induced gvbd. | 1981 | 6263509 |
| translation of three mouse hepatitis virus strain a59 subgenomic rnas in xenopus laevis oocytes. | we have purified the seven virus-specific rnas which were previously shown to be induced in sac(-) cells upon infection with mouse hepatitis virus strain a59 (w. j. m. spaan, p. j. m. rottier, m. c. horzinek, and b. a. m. van der zeijst, virology 108:424-434, 1981). the individual rnas, prepared by agarose gel electrophoresis of the polyadenylated rna fraction from infected cells, were obtained pure, except for the preparations of rnas 4, 5, and 6, which contained some contamination of rna 7. th ... | 1981 | 6264100 |
| calmodulin triggers the resumption of meiosis in amphibian oocytes. | the calcium-binding protein, calmodulin, has been purified from xenopus laevis oocytes. this 18,500-dalton protein, pl 4.3, has two high-affinity calcium-binding sites per mole protein having a dissociation constant of 2.8 x 10(-6) m. full-grown xenopus oocytes, arrested in late g2 of the meiotic cell cycle, resumed meiosis when microinjected with 60-80 ng (3-4 pmol) of calmodulin in the form of a calcium-calmodulin complex. the timing of the meiotic events in these recipient oocytes was the sam ... | 1981 | 6265465 |
| the organization of the histone genes in the genome of xenopus laevis. | we have studied the organization of the histone genes in the dna from several individuals of xenopus laevis. for that purpose, southern blots of genomic dna, that was digested with several restriction enzymes, were hybridized with radioactively labeled dna fragments from clone x1-hi-1 (14), containing genes for xenopus histones h2a, h2b, h3 and h4. in the dna of all animals that were screened we found a major repeating unit of 14 kilobasepairs, which contains genes for histones h2a, h2b, h3 and ... | 1981 | 6265869 |
| specific binding of a prokaryotic ribosomal protein to a eukaryotic ribosomal rna: implications for evolution and autoregulation. | ribosomal protein l1 from the prokaryote escherichia coli has been shown to form a specific complex with 26s ribosomal rna from the eukaryote dictyostelium discoideum. the segment of dictyostelium rrna protected from ribonuclease digestion by l1 and the corresponding region in dictyostelium rdna were investigated by nucleotide sequence analysis, and an analogous section in rdna from xenopus laevis was identified. when the l1-specific segments from eukaryotic rrna were compared with those from pr ... | 1981 | 6265904 |
| effect of a methyl-transferase inhibitor, 5'-deoxy'5'-s-isobutyl-thioadenosine (siba) on camp level and progesterone induced meiosis reinitiation in xenopus laevis oocytes. | | 1981 | 6268063 |
| mitochondrial number, cytochrome oxidase and succinic dehydrogenase activity in xenopus laevis oocytes. | an estimate has been made of the numbers of mitochondria in the mitochondrial cloud (balbiani body) of xenopus laevis oocytes ranging in size from 50 to 250 micrometers. the mitochondrial number is expressed in terms of a 'standard' organelle measuring 2 micrometers in length and 0.2 micrometer in diameter and is derived by measurements on electron micrographs of sections through the cloud. it is found that the amount of mitochondrial material rises very rapidly as the oocyte grows in size. at t ... | 1981 | 6268730 |
| isolation and characterization of genomic clones covering the chicken vitellogenin gene. | a series of overlapping recombinant clones, which cover the vitellogenin gene, has been isolated from a phage-lambda linked chicken gene library. the dna of the overlapping clones spans 28 kb of contiguous dna sequences in the chicken genome. electron microscopic analysis of hybrids between vitellogenin mrna and the genomic clones indicates that the chicken vitellogenin gene has a length of approximately 22 kb, about 3.8 times the size of the mrna. the mrna sequence is interrupted by at least 33 ... | 1981 | 6269078 |
| replication of sv40 chromatin in extracts from eggs of xenopus laevis. | simian virus 40 (sv40) nucleoprotein complexes were prepared from lytically infected cells and used as primer-templates for dna replication in protein extracts from xenopus eggs. we found that nucleoprotein containing replicating sv40 dna served as primer-template while nucleoprotein with nonreplicating sv40 dna was ineffective. in vitro dna synthesis begins with short dna fragments ("okazaki fragments") which are, in later steps, joined to give unit length sv40 dna strands, suggesting that in v ... | 1981 | 6269093 |
| involvement of camp in the cytoplasmic control of meiotic cell division in xenopus laevis oocytes. | 1) there is a large body of evidence for an inhibitory role for camp in progesterone induced meiosis in amphibian oocytes consistent with its known inhibitory activity in mammalian oocytes (5,26). it implies that the action of steroid hormones in this particular tissue is mediated by modifications of camp levels within the cell. 2) bacterial toxins have proved to be useful reagents in the investigation of the regulatory role of cyclic nucleotides in the resumption of cell division in amphibian o ... | 1981 | 6269393 |
| dna topoisomerase i from mitochondria of xenopus laevis oocytes. | activity of dna topoisomerase i has been characterized in extracts of mitochondria purified from xenopus laevis oocytes. several lines of evidence have been obtained for the intramitochondrial localization of the enzyme. the mitochondria-associated of dna topoisomerase i represents 1% of the activity recovered from a total ovary population of oocytes. the enzymes has been purified by deae-cellulose, phosphocellulose and double-stranded dna cellulose chromatography and its properties compared to ... | 1981 | 6269855 |
| quantitation of the accumulation of histone messenger rna during oogenesis in xenopus laevis. | | 1981 | 6269929 |
| transcription and translation of the herpes simplex virus type 1 thymidine kinase gene after microinjection into xenopus laevis oocytes. | the hybrid plasmid ptk1 consists of the herpes simplex virus type 1 (hsv-1) bamhi p fragment, which contains the thymidine kinase (tk) gene, inserted into the vector pat 153. when ptk1 dna was microinjected into nuclei of xenopus laevis oocytes, functional hsv-1-specific tk was produced, showing that transcription and translation of the gene occurred. investigation of ptk1-specific rna by "southern' blot hybridization revealed that all regions of the hybrid plasmid were transcribed by rna polyme ... | 1981 | 6270258 |
| calmodulin is involved in the first step of oocyte maturation: effects of the antipsychotic drug fluphenazine and of anticalmodulin antibodies on the progesterone-induced maturation of xenopus laevis oocyte. | specific anticalmodulin antibodies were microinjected into full-grown xenopus laevis oocyte, and it is shown that in ovo blockade of the complex ca2+-calmodulin accelerates the kinetics of progesterone-induced maturation, even though the molar ratio of antibody binding sites to total calmodulin was only 0.16. addition of 200 microm fluphenazine to the oocyte incubation medium resulted in a similar acceleration of steroid-induced maturation. neither protein kinase inhibitor (pki) nor maturation p ... | 1981 | 6274518 |
| primary structure of the histone h3 and h4 genes and their flanking sequences in a minor histone gene cluster of xenopus laevis. | | 1981 | 6274702 |
| adenosine 3' :5' monophosphate receptor sites in xenopus laevis oocytes. | adenosine 3':5' cyclic monophosphate (cyclic amp) binds to proteins present in the 100,000 g supernatant fractions of full-grown oocytes of xenopus laevis. optimal ph for the binding is 4.0. two receptor binding sites have been characterized by density gradient centrifugation as peaks with sedimentation constants of 4.6 s and 5.9 s. the apparent dissociation constants for the two cyclic amp binding sites are 7 nm and 40 nm. the total cyclic amp binding capacity of oocyte cytosol is 15.8 +/- 2.2 ... | 1981 | 6276257 |
| deletion of the 3' half of the yeast trna-leu3 gene does not abolish promotor function in vitro. | the promotor function of the 3' and 5' half trna sequences in the yeast trna-leu3 gene has been studied by in vitro transcription in xenopus laevis germinal vesicle (gv) extracts. truncation of the dna template within the trna intervening sequence by hpa i abolishes transcription. however, separation of the trna gene halves by insertion of a 300 bp dna fragment at the hpa i site does not affect the promoter efficiency. further, the complete sequence of the 3' half of the trna is not necessary fo ... | 1981 | 6277504 |
| biosynthesis of pairs of peptides related to melanotropin, corticotropin and endorphin in the pars intermedia of the amphibian pituitary gland. | this study concerns the biosynthesis of a number of peptides in the neurointermediate lobe of the pituitary gland of the aquatic toad, xenopus laevis. using pulse-chase incubations in vitro and high-performance liquid chromatographic analysis, it could be shown that these peptides are synthesized through processing of a prohormone, pro-opiomelanocortin; all peptides were released into the incubation medium. on the basis of electrophoretic analysis, selective amino acid incorporation and immunopr ... | 1982 | 6277629 |
| in vitro transcription of a cloned mouse ribosomal rna gene. | an in vitro transcription system which utilizes cloned mouse ribosomal rna gene (rdna) fragments and a mouse cell extract has been developed. rna polymerases i is apparently responsible for this transcription as evidenced by the complete resistance to a high concentration (200 micrograms/ml) of alpha-amanitin. run-off products obtained with three different truncated rdna fragments indicated that rna was transcribed from a unique site of rdna. the s1 nuclease protection mapping of the in vitro pr ... | 1981 | 6278446 |
| 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 |
| messenger rnas of mouse hepatitis virus a59: isolation and characterization, translation in xenopus laevis oocytes of rnas 3, 6 and 7, uv target sizes of the transcription templates. | | 1981 | 6278883 |
| 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 |
| the rise and fall of electrical excitability in the oocyte of xenopus laevis. | 1. an electrically excited (gated) sodium selective channel has been found in the xenopus laevis oocyte, a cell membrane previously considered non-excitable. 2. the channel is produced by prolonged depolarization of the membrane and is removed by prolonged repolarization. both processes are very dependent on temperature and potential. 3. once produced, the channel can be opened and closed electrically, but does not show inactivation as is found in other sodium selective channels. 4. the sodium s ... | 1981 | 6286961 |
| mrna- and dna-directed synthesis of herpes simplex virus-coded exonuclease in xenopus laevis oocytes. | microinjection of herpes simplex virus (hsv)-infected cell mrna into xenopus laevis oocytes resulted in the production of a new exonuclease activity. this enzyme strongly resembled the hsv alkaline exonuclease in many biochemical properties, and hybrid-arrested translation studies showed that it was virus coded, mapping at 0.080 to 0.185 genome map units. exonuclease mrna had a size and genome location equivalent to the mrna encoding v185 in reticulocyte lysates, suggesting that v185 is the exon ... | 1982 | 6287023 |
| chromosome-bound mitotic factors: release by endonucleases. | additional evidence is presented to support our recently reported conclusion that the mitotic factors of mammalian cells, which induce germinal vesicle breakdown and chromosome condensation when injected into fully grown xenopus laevis oocytes, are localized on metaphase chromosomes. chromosomes isolated from mitotic hela cells were further purified on sucrose gradients and digested for varying periods with either the micrococcal nuclease or dnase ii. at each time point of digestion the amount o ... | 1982 | 6287433 |
| immunohistochemical demonstration of tsh-, lh- and acth-cells in the hypophysis of tadpoles of xenopus laevis d. | by use of the immunofluorescence technique tsh-, lh- and acth-cells were localized in the hypophysis of tadpoles of xenopus laevis. the first signs of the activity of these cells were observed in early stages of the development, i.e., stage 39 for acth, and stage 42 for tsh and lh. | 1982 | 6288250 |
| cloning in a cosmid vector of complete 37 kb and 25 kb ribosomal dna repeat units from the chicken. | dna fragments of up to 40 kb containing rrna-coding sequences have been isolated from a chicken liver dna library prepared in the cosmid phc79. characterization of the cloned dna by r-loop and restriction mapping has shown that there are two size classes of repeat unit, one of 37 kb and one of 25 kb, the larger of which is a family of units which vary slightly in size. these two classes were shown to be present in the dna of a single chicken. the size of the internal transcribed spacer in the ch ... | 1982 | 6289899 |
| a restriction map of xenopus laevis mitochondrial dna. | the mitochondrial dna from xenopus laevis is a 17.4 x 10(3)-base-pair circular dna molecule. the mapping of this dna, using 19 different restriction endonucleases is reported here. the sites are as follows: 1 for bamhi, psti, saci, sali, bali; 2 for bglii, sacii, ecori, clai, 3 for xhoi, 4 for avai, xbai, pvuii, 5 for hindiii, 6 for hhai, bcli, hpai, 10 for avaii and 11 for hincii. the same sites (except for one of the two clai sites) are observed in the molecule cloned in pbr322 dna. the fragme ... | 1982 | 6290211 |
| adenylate cyclase in xenopus laevis oocytes: characterization of the progesterone-sensitive, membrane-bound form. | progesterone-induced reinitiation of meiosis in xenopus laevis oocytes involves a decrease in camp level. in these cells, adenylate cyclase is compartmentalized, with 25-30% in the plasma membrane fraction p-10000 (sedimenting at 10000 x g) and greater than 50% in the cytosol. soluble adenylate cyclase appears not to be regulated via a gtp-binding regulatory protein (g/f) and is insensitive to progesterone. in contrast, membrane-bound adenylate cyclase seems to be linked to g/f, since it is stim ... | 1982 | 6290296 |
| methylation of simian virus 40 hpa ii site affects late, but not early, viral gene expression. | dna methylation has been correlated with reduced gene expression in a number of studies, although evidence for a casual link between the two events has been lacking. because microinjection of simian virus 40 (sv40) dna into the nucleus of xenopus laevis oocytes results in the synthesis of both early and late viral gene products, it was possible to test whether a specific methylation event can affect gene expression. the single sv40 hpa ii site at 0.72 sv40 map units was specifically methylated w ... | 1982 | 6291026 |
| microinjected progesterone reinitiates meiotic maturation of xenopus laevis oocytes. | microinjection of progesterone dissolved in paraffin oil induces the reinitiation of meiotic maturation in the xenopus oocyte; 50% maturation is obtained when 50 nl of a 50 microm solution is microinjected into the oocyte. the kinetics of the response to microinjected progesterone are similar to the kinetics of response to externally applied hormone. when an aqueous solution of progesterone is microinjected instead of an oil solution, maturation is never observed, a result which confirms previou ... | 1982 | 6291050 |
| initiation of replication at specific origins in dna molecules microinjected into unfertilized eggs of the frog xenopus laevis. | initiation of dna replication at specific origins was observed by electron microscopy after microinjection of pxlr11, pxlr14 or col e1 plasmid dna molecules into unfertilized eggs of the frog, xenopus laevis. these results are in apparent contradiction with published reports (harland and laskey, cell 21, 761-771, 1980; laskey and harland, cell 24, 283-284, 1981) that specific origin sites were not used in xenopus laevis eggs. we suggest that eucaryotic origins exist that both increase the probab ... | 1982 | 6291769 |
| interaction of steroids and growth factors with the plasma membrane in the induction of oocyte maturation in xenopus laevis. | | 1982 | 6292941 |
| nad-glycohydrolase activity in xenopus laevis oocytes and early embryos. | | 1982 | 6293487 |
| simple, efficient in vitro synthesis of capped rna useful for direct expression of cloned eukaryotic genes. | a simple and efficient method for direct in vitro synthesis of capped transcripts of cloned eukaryotic genes is described. as an example capped transcripts were made from a plasmid containing the human fibroblast interferon gene cloned under the control of a prokaryotic promoter. these transcripts were translated in vivo in xenopus laevis oocytes and in vitro in reticulocyte and in wheat germ cell-free protein synthesizing systems. | 1982 | 6294601 |
| vitellogenin genes a1 and b1 are linked in the xenopus laevis genome. | genomic clones containing the xenopus laevis vitellogenin gene b1 have been isolated from dna libraries and characterized by heteroduplex mapping in the electron microscope, restriction endonuclease analysis, and in vitro transcription in a hela whole-cell extract. sequences from the 3'-flanking region of the previously isolated a1 vitellogenin gene were found in the 5'-flanking region of this b1 gene. thus, the two genes are linked, with 15.5 kilobase pairs of dna between them. their length is ... | 1982 | 6294657 |
| 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 |
| in vivo biosynthesis of melanotropins and related peptides in the pars intermedia of xenopus laevis. | to study in vivo biosynthesis of pars intermedia peptides in xenopus laevis, [3h]lysine was administered by an osmotic minipump via a cannula inserted near the pituitary gland. following extraction of the neurointermediate lobe, high-performance liquid chromatography was used to separate the newly synthesized peptides. in black-background adapted animals, [3h]lysine was incorporated into a number of peptides. the elution characteristics of these peptides corresponded exactly with those of peptid ... | 1983 | 6298059 |
| in vivo catenation and decatenation of dna. | we have noted previously that when circular, but not linear, dna or chromatin was injected into xenopus laevis oocytes, much of it went through an intermediate form in which it did not readily enter an agarose gel; after a few hours, it reappeared as monomer dna that had acquired its full complement of nucleosomes (t. j. miller and j. e. mertz, mol. cell. biol. 2:1581-1593, 1982). we determined, using electron microscopy and a variety of biochemical techniques, the structure of this aggregated m ... | 1983 | 6298603 |
| 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 |
| 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 |
| 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 |
| temperature- and structure-dependent interaction of pyrethroids with the sodium channels in frog node of ranvier. | (1) the interaction of a series of pyrethroid insecticides with the na+ channels in myelinated nerve fibres of the clawed frog, xenopus laevis, was investigated using the voltage clamp technique. (2) out of 11 pyrethroids 9 insecticidally active compounds induce a slowly decaying na+ tail current on termination of a step depolarization, whereas the na+ current during depolarization was hardly affected. these tail currents are most readily explained by a selective reduction of the rate of closing ... | 1983 | 6299340 |
| early increase of a 105,000-dalton phosphoprotein during meiotic maturation of xenopus laevis oocyte. | in ovo [32p] phosphoproteins were analyzed during meiotic maturation of xenopus laevis oocytes. a phosphoprotein of 105,000-dalton was found to increase early (one hour) after progesterone induction of meiosis. the pure heat-stable inhibitor (pki) of camp-dependent protein kinase, which induces maturation, was microinjected into oocytes. again the early increase in the 105,000-dalton [32p] phosphoprotein occurred. the burst in protein phosphorylation, which takes place at the period of germinal ... | 1983 | 6299401 |
| multiple heterogeneities in the transcribed spacers of ribosomal dna from xenopus laevis. | ribosomal dna (rdna) from xenopus laevis contains several heterogeneities in all three transcribed spacers, as revealed by analysis of cloned and uncloned amplified rdna from oocytes and cloned chromosomal rdna from erythrocytes. heterogeneities include single base changes and length variants of one to several nucleotides. sites of variation are widely but non-uniformly distributed, some occurring only a short distance outside the boundaries of the rrna coding regions. no two transcription units ... | 1983 | 6300760 |
| post-transcriptional modification of the wobble nucleotide in anticodon-substituted yeast trnaargii after microinjection into xenopus laevis oocytes. | an enzymatic procedure for the replacement of the icg anticodon of yeast trnaargii by ncg trinucleotide (n = a, c, g or u) is described. partial digestion with s1-nuclease and t1-rnaase provides fragments which, when annealed together, form an "anticodon-deprived" yeast trnaargii. a novel anticodon, phosphorylated with (32p) label on its 5' terminal residue, is then inserted using t4-rna ligase. such "anticodon-substituted" yeast trnaargii are microinjected into the cytoplasm of xenopus laevis o ... | 1983 | 6300762 |
| regulation of 17 beta-hydroxysteroid oxydoreductase of the xenopus laevis follicle by gonadotropin and prolactin. | ovarian follicles of xenopus laevis, incubated in vitro actively metabolized radioactive 4-androstene-3, 17-dione to testosterone, indicating the presence of a 17 beta-hydroxysteroid-oxydoreductase (17 beta-hsor). this enzymatic activity was found to be solely localized in the follicular envelopes. in vitro treatment of follicles with hcg for 2 hr induced a 40% decrease of the 17 beta-hsor activity. the gonadotropin-induced inhibition was dose-dependent and only observed with gonadotropic lh-lik ... | 1983 | 6301934 |
| can dna methylation regulate gene expression? | the e2a region of the ad2 genome encodes the ad2-specific dbp. an inverse correlation between the level of dna methylation at the 5'-cc*gg-3' sites of the e2a region and the extent of expression of dbp has been demonstrated in ad2-transformed hamster cell lines (vardimon et al. 1980). four different leaders are used in the transcription of the e2a region in cells productively infected with ad2. the leader located at coordinate 75 on the viral genome is used early after infection and the other th ... | 1983 | 6302751 |
| steroid-membrane-adenylate cyclase interactions during xenopus laevis oocyte meiosis reinitiation: a new mechanism of steroid hormone action. | progesterone acts physiologically on xenopus laevis oocyte meiosis reinitiation in interacting with plasma membrane. hormonal studies indicate a specific "receptor-like" structure. the involvement of membrane adenylate cyclase activity which is selectively decreased by progesterone is described in intact oocytes as well as in a cell-free membrane containing system. the participation of ca2+ changes and of phospholipid components of membrane is analyzed. we discuss the possibility that the proges ... | 1983 | 6303813 |
| functional integrity of desensitized beta-adrenergic receptors. | the adenylate cyclase-coupled beta 2-adrenergic receptor of the frog erythrocyte has served as a useful model system for elucidating the mechanisms of catecholamine-induced densensitization. in this system, it has been previously demonstrated that agonist-induced refractoriness is associated with sequestration of the beta-adrenergic receptors in vesicles away from the cell surface and from their effector unit, the adenylate cyclase system (stadel, j.m., strulovici, b., nambi, p., lavin, t.n., br ... | 1983 | 6304039 |
| changes in water proton relaxation times and in nuclear to cytoplasmic element gradients during meiotic maturation of xenopus oocytes. | fully grown oocytes 1.2 mm in diameter were removed from xenopus laevis ovaries and were exposed to progesterone (2.5 micrograms/ml in ringer's solution) to induce completion of the first maturation division or germinal vesicle breakdown (gvbd). this process required 5.5 +/- 0.5 hr. neither oocyte volume nor water content was observed to change throughout maturation. at selected times, the oocytes were quick frozen in liquid propane and cryosectioned. the sections were freeze-dried, and analyzed ... | 1983 | 6304127 |
| vitellogenin b2 gene in xenopus laevis: isolation, in vitro transcription and relation to other vitellogenin genes. | the isolation of the four xenopus laevis vitellogenin genes has been completed by the purification from a dna library of the b2 gene together with its flanking sequences. the overlapping dna fragments analyzed cover 34 kilobases. the b2 gene which has a length of 17.5 kilobases was characterized by heteroduplex and r-loop mapping in the electron microscope and by in vitro transcription in a hela whole-cell extract. its structural organization is compared with that of the closely related b1 gene ... | 1983 | 6304616 |
| the expression of prokaryotic trna genes in frog oocytes. | a trna gene cluster in salmonella typhimurium includes the genes for trnaarg, trnahis, trna1leu and trnapro. dna clones were constructed with different portions of this trna gene cluster. these clones were microinjected into the nuclei of xenopus laevis oocytes and assayed for expression. two of the bacterial trna genes (trnaarg and trnapro) are transcribed at high rates and the primary transcripts are processed into mature trnas. transcription and processing are largely independent of whether t ... | 1983 | 6304627 |
| ribosomal 5s genes in relation to c-value in amphibians. | we have measured the amount of 5s-ribosomal dna in the genomes of xenopus laevis, triturus cristatus carnifex and ambystoma mexicanum, three species of amphibians which have widely different c-values. our best estimate is that these organisms have about 24,000, 32,000 and 61,000 5s-genes per haploid genome respectively. a trend to increasing 5s gene copynumber with increasing c-values in amphibians is apparent, probably linked to the need to supply more ribosomes to the larger cells which are as ... | 1983 | 6304650 |
| isolation of novel human genomic dna clones related to human interferon-beta 1 cdna. | southern blot-hybridization analyses of human dna (from namalwa lymphoblastoid cells) digested with the restriction endonuclease ecori were carried out under optimal conditions with two human fibroblast interferon (ifn-beta 1) cdna probes, pd19 and pd24, which contain ifn-beta 1 inserts 0.8 and 0.7 kilobase (kb) long, respectively. the analyses revealed the presence of several hybridizable dna fragments, including two of lengths 6.8 and 5.5 kb, in addition to the classical ifn-beta 1 genomic dna ... | 1983 | 6304727 |
| evidence for two functional regions in the xenopus laevis rna polymerase i promoter. | | 1983 | 6305588 |
| the development of competence for meiotic maturation during oogenesis in xenopus laevis. | meiotic maturation of large, 1.2-1.4 mm in diameter, stage vi oocytes of xenopus laevis can be induced to mature in vitro by exposure to progesterone or by microinjection of maturation-promoting factor (mpf). small, 0.95 mm in diameter, stage iv oocytes do not respond to progesterone but do undergo germinal vesicle breakdown (gvbd) in response to microinjection of mpf. the possibility that small oocytes are nonresponsive to progesterone due to a specific defect in an event known to occur with la ... | 1983 | 6305745 |
| the genomic organization of dispersed trna and 5 s rna genes in xenopus laevis. | the 5 s dnas and several tdnas of xenopus laevis reside primarily in large clusters of tandem repeating units. we have discovered that a substantial number of these genes, along with portions of their adjacent spacer sequences, are also located in dispersed genomic locations apart from the major clusters. this was accomplished by "null-digesting" total genomic dna with restriction enzymes that do not cut within the x. laevis tdna or 5 s dna major repeats. the tdna and 5 s dna main clusters there ... | 1983 | 6305940 |
| the complete nucleotide sequence of the major adult beta globin gene of xenopus laevis. | we present the complete nucleotide sequence of the major beta globin gene of xenopus laevis with 127 nucleotides of sequence upstream of the gene and 212 nucleotides downstream. the start point of transcription was determined by s1 mapping and primer extension and the site of polyadenylation by comparison with the mrna sequence determined from a cdna clone. comparison of the x. laevis sequence with other genes transcribed by rna polymerase ii reveals conserved features in the 5' flanking, 5' non ... | 1983 | 6305990 |
| nuclease sensitivity and dna methylation in estrogen regulation of xenopus laevis vitellogenin gene expression. | estrogen activates transcription of the vitellogenin genes in livers of male xenopus laevis. we have examined the conformation of the vitellogenin genes in chromatin and the methylation state of one vitellogenin gene during the process of estrogen stimulation and withdrawal. sensitivity of the vitellogenin genes to dnase i digestion parallels transcription. the vitellogenin genes are insensitive to dnase i digestion in unstimulated liver cells, become more sensitive to dnase i digestion followin ... | 1983 | 6306003 |
| proliferation in vitro of melanophores from xenopus laevis. | melanophores of wild-type and periodic albino mutants of xenopus laevis were successfully cultured in vitro. they proliferated in the presence of alpha-melanocyte-stimulating hormone (alpha-msh or cyclic adenosine monophosphate (camp) at a doubling time of 8-10 days. these proliferating melanophores retained their phenotypes, ability to synthesize melanin, and melanin-dispersing response to msh stimulation. neither depigmentation nor selective cell death of periodic albino melanophores was obser ... | 1983 | 6306135 |
| muscle activity and the loss of electrical coupling between striated muscle cells in xenopus embryos. | the gap junctions between embryonic striated muscle cells are lost during development. the time course of their elimination has been examined with electrophysiological techniques in myotomes of xenopus laevis embryos. gap junctions were detected by the passage of electronic current or the fluorescent dye, lucifer yellow, from one muscle cell to another. these tracers only spread to neighboring cells when injected intracellularly. all the muscle cells are electrically coupled at stage 24 when neu ... | 1983 | 6306176 |
| nucleotide sequence of the genetically labile repeated elements 5' to the origin of mouse rrna transcription. | we have determined the complete nucleotide sequence of a cloned balb/c mouse rdna nts fragment containing 13 tandem copies of a 135 bp subrepeating segment. this repetitious region (vrdna) lies close to the origin of ribosomal rna transcription. analyses of these vrdna subrepeats from balb/c and a related species, mus pahari, reveal regions of inverted repeat dna as well as large poly t tracts, either of which may be significant to the generation of the high levels of vrdna copy number variation ... | 1983 | 6306564 |
| transcription of cloned moloney murine leukemia proviral dna injected into xenopus laevis oocytes. | we have microinjected genomic dna clones containing the moloney murine leukemia virus (m-mulv) proviral genome and flanking mouse sequences from mov-3, mov-7 and mov-10 mice into xenopus laevis oocytes and analyzed the virus-specific transcription and translation products. these mouse strains carry a proviral genome copy of m-mulv in their germ line at different chromosomal positions and differ from each other with respect to expression of the proviral genome. we show here that the different m-m ... | 1983 | 6306570 |
| tail muscle hydrolases during metamorphosis of the anuran tadpole. i. histochemical studies. | naphthylamidase, beta-glucuronidase and trimetaphosphatase have been studied histochemically in the tail muscles of rana catesbeiana, rana japonica and xenopus laevis tadpoles. during the early stages of growth, tadpole tail muscles showed very low activity of these hydrolases, whereas during the prometamorphic and metamorphic stages, they exhibited a marked increase in enzyme activity. this was localized in the subepidermal and subnotochordal mesenchymous tissue and in the myoseptum, i.e. betwe ... | 1983 | 6307934 |
| phosphoinositide metabolism in the retina: localization to horizontal cells and regulation by light and divalent cations. | isolated retinas from xenopus laevis incorporated greater amounts of [3h]inositol and 32pi into phosphoinositides when incubated in light than did control retinas incubated in the dark. inositol was primarily incorporated into phosphatidylinositol (83-86%), while phosphate labeled the polyphosphoinositides (72-79%). the incorporation of radioactive glycerol, serine, choline, or ethanolamine into retinal lipids was unaffected by light. following incubation with [3h]inositol, the cell type involve ... | 1983 | 6308171 |
| dna sequence of the xenopus laevis mitochondrial heavy and light strand replication origins and flanking trna genes. | we have determined the primary structure of the two regions of the xenopus laevis mitochondrial genome which encompass the origins of heavy (h) and light (l) strand replication. the first segment, which consists of 2398 nucleotides, contains the displacement loop (d-loop), the trna genes for threonine, proline and phenylalanine, the origin of h-strand replication, and the promoters of h- and l-strand transcription. the second segment, which consists of 447 nucleotides, contains the l-strand repl ... | 1983 | 6308566 |
| reconstitution of beta-adrenergic receptors in lipid vesicles: affinity chromatography-purified receptors confer catecholamine responsiveness on a heterologous adenylate cyclase system. | the binding function of purified receptors can be assessed with radioligands, but the interaction of receptors with their biochemical effectors has not been amenable to direct study. toward this end, procedures have been developed for directly demonstrating functionality of purified beta-adrenergic receptor preparations. digitonin-solubilized beta-adrenergic receptors from frog erythrocytes or rat lung were purified approximately equal to 100- to 5,000-fold by affinity chromatography and inserte ... | 1983 | 6308659 |
| direct radioactive labelling of poly(adp-ribose) in developing xenopus laevis embryos. | it has not previously been possible to label the nuclear protein modification poly(adp-ribose) directly from nad because of the impermeability of the cell membrane. we have overcome this important problem by micro-injection of radioactively labelled nad into xenopus laevis early embryos. the polymer was identified and then quantified by its insensitivity to dnaase, rnaase, and spleen phosphodiesterase and by the chromatographic mobility of the products of digestion with snake-venom phosphodieste ... | 1983 | 6309267 |
| structure and evolution of the xenopus laevis albumin genes. | the 68k and 74k albumin genes of xenopus laevis arose by duplication approximately 30 million years ago. electron microscopic analysis showed that both genes contain 15 coding sequences. the lengths of corresponding coding sequences are almost identical and are extremely similar to those of mammalian albumin genes. a block of four coding sequences, which in mammals codes for one protein domain, is repeated three times. the corresponding introns are usually different in length and have therefore ... | 1983 | 6310119 |
| dnasei-hypersensitive sites at promoter-like sequences in the spacer of xenopus laevis and xenopus borealis ribosomal dna. | we have detected a dnasei hypersensitive site in the ribosomal dna spacer of xenopus laevis and xenopus borealis. the site is present in blood and embryonic nuclei of each species. in interspecies hybrids, however, the site is absent in unexpressed borealis rdna, but is present normally in expressed laevis rdna. hypersensitive sites are located well upstream (over lkb) of the pre-ribosomal rna promoter. sequencing of the hypersensitive region in borealis rdna, however, shows extensive homology w ... | 1983 | 6310495 |
| 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 |
| 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 |