| molecular cloning of human immune interferon cdna and its expression in eukaryotic cells. | starting with mrna derived from staphylococcal enterotoxin a induced human splenocytes, dsdna was synthesized and inserted into unique bamhi site of the eukaryotic expression vector psv529 (1). a recombinant plasmid containing human immune interferon (ifn-gamma) cdna was identified by hybridization of plasmid inserted dna bound onto nitrocellulose filters with mrna derived from sea-induced splenocytes, translation of the eluted rna in xenopus laevis oocytes and assaying for ifn activity. plasmid ... | 1982 | 6176945 |
| secretory proteins induced in human fibroblasts under conditions used for the production of interferon beta. | human fibroblast cells treated with a combination of inhibitors of protein and rna synthesis [cycloheximide and actinomycin d as used to superinduce interferon beta (ifn-beta)] secrete two proteins with molecular masses of 22000 and 27000 kilodaltons (called 22-kdal and 27-kdal) that are precipitable with an antiserum raised against impure ifn-beta but are antigenically distinct from ifn-beta 1. translation in vitro of mrna extracted from human fibroblast cells induced for the production of ifn- ... | 1982 | 6178110 |
| persistence of nonribosome bound 5 s rna in full-grown oocytes of xenopus laevis. | | 1982 | 6178636 |
| parallel changes in protein synthesis and messenger rna content in growing and resting epithelial cells of xenopus laevis. | the regulation of cell growth can be achieved at many levels but ultimately the regulatory factors must alter protein synthesis since growing cells always exhibit an increased rate of protein synthesis compared to resting cells. some studies using growing and nongrowing mammalian cells have shown that the rate of protein synthesis is directly dependent on mrna content. other studies have shown that growing the resting cells have similar amounts of mrna and that protein synthesis is regulated by ... | 1982 | 6178747 |
| development of the marginal zone in the rhombenecephalon of xenopus laevis. | the marginal zone is the most superficial component of the developing central nervous system. in this study we describe the pattern of formation of the marginal zone in xenopus laevis as seen with the light microscope and correlate its appearance with developing axon bundles seen with the electron microscope. the marginal zone was first identified at stage 26 on the ventrolateral aspects of the neural tube in restrictive foci throughout the medulla. by stage 28 this presumptive fiber area had ex ... | 1982 | 6179577 |
| the determination of the instantaneous velocity of axonally transported organelles from filmed records of their motion. | a computational procedure is described for obtaining reproducible, low noise estimates of the instantaneous velocity of axonally transported organelles. axonally transported organelles were detected in myelinated nerve fibers from xenopus laevis by dark-field microscopy. the motion of the organelles was recorded on motion picture film at 3 frames/s, and the position of organelles travelling in the retrograde direction was obtained as a pair of x (axial) and y (transverse) coordinates at each 0.3 ... | 1982 | 6179589 |
| transcription of a gene for human u1 small nuclear rna. | transcription of u1 small nuclear rna from a 592 bp fragment of human dna was analyzed in vivo and in vitro. when injected into xenopus laevis oocyte nuclei, the cloned dna is transcribed by rna polymerase ii to make human u1 snrna. thus the sequences of this fragment are sufficient for expression of the u1 snrna gene. moreover, injection of templates carrying deletions of flanking sequences demonstrates that the dna sequences required for in vivo transcription are located at least 100 nucleotid ... | 1982 | 6179630 |
| cellular titers and subcellular distributions of abundant polyadenylate-containing ribonucleic acid species during early development in the frog xenopus laevis. | the distribution of cytoplasmic messenger ribonucleic acids (rnas) in translationally active polysomes and inactive ribonucleoprotein particles changes during early development. cellular levels and subcellular distributions have been determined for most messenger rnas, but little is known about how individual sequences change. in this study, we used hybridization techniques with cloned sequences to measure the titers of 23 mitochondrial and non-mitochondrial polyadenylate-containing [poly(a)+]rn ... | 1981 | 6180297 |
| forskolin increases camp and inhibits progesterone induced meiosis reinitiation in xenopus laevis oocytes. | the diterpene, forskolin, is a potent and reversible inhibitor of progesterone-induced meiosis in xenopus laevis oocytes (ed50 of inhibition approximately 3 microm). forskolin alone increases camp concentration in oocytes, but, unlike with cholera toxin treatment, there is no lag phase, and reversibility is obtained by washing the cells. progesterone decreases the forskolin effect on camp accumulation, but camp concentration remains above the level observed in oocytes treated with progesterone a ... | 1982 | 6180891 |
| medusoid fibril bodies: a novel type of nuclear filament of diameter 8 to 12 nm with periodic ultrastructure demonstrated in oocytes of xenopus laevis. | | 1982 | 6180897 |
| mouse interferon messenger rna: characterization of the xenopus laevis oocyte translation product. | | 1982 | 6181741 |
| isolation and characterization of ifn-gamma mrna derived from mitogen-induced human splenocytes. | human splenocytes from large cultures (5 1) were stimulated with staphylococcus enterotoxin a (sea). after 2.5 d of conditioning, poly a+rna was isolated from these cultures and its in-vitro translational capacity was evaluated in a wheat germ extract. injection of the rna into xenopus laevis oocytes yielded a low but reproducible amount of ifn activity, which was neutralizable only by an antiserum to gamma interferon (ifn-gamma) and not by antisera to alpha interferon (ifn-alpha) and/or beta in ... | 1982 | 6182256 |
| a study of the motion of organelles which undergo retrograde and anterograde rapid axonal transport in xenopus. | 1. axonally transported organelles were detected optically in myelinated axons from xenopus laevis at room temperature (21-23 degrees c). details of the motion of organelles which were transported in the retrograde and anterograde directions were studied using filmed records.2. a group of 133 organelles with a mean retrograde velocity of 0.91 mum/sec was compared with a group of thirty-nine organelles with a mean anterograde velocity of 0.93 mum/sec.3. averaged power spectra of the positional de ... | 1982 | 6182282 |
| translation in vitro of rna from the human malarial parasite plasmodium falciparum. | rna has been isolated from the human malarial parasite, plasmodium falciparum, and translated in vitro using two systems: rabbit-reticulocyte lysate and xenopus laevis oocytes. polypeptides are synthesized that are characteristic of the parasite isolate and the developmental stage from which the rna was purified. many of these polypeptides are precipitated by antibody from an immune monkey. analysis of the primary structure of these polypeptides should give the information necessary to produce a ... | 1982 | 6182932 |
| regulation of protein synthesis and accumulation during oogenesis in xenopus laevis. | | 1982 | 6183158 |
| divergence of the two albumins of x. laevis. evidence for the glycosylation of the major 74k albumin. | the mrnas coding for the 68,000 and 74,000 dalton serum albumins of xenopus laevis were purified by hybridisation to their corresponding cloned cdna and translated using the reticulocyte lysate. the primary translational product of the 68,000 dalton albumin has a molecular weight of 70,000 daltons suggesting that it is synthesised with a signal peptide which is cleaved during secretion. in contrast, the primary translational product of the 74,000 dalton albumin has a molecular weight of 72,000 d ... | 1982 | 6184256 |
| nucleocytoplasmic distribution of snrnps and stockpiled snrna-binding proteins during oogenesis and early development in xenopus laevis. | the distribution of small nuclear ribonucleoprotein particles containing u snrnas (u snrnps) during oogenesis and early development in xenopus was analyzed with a lupus antibody (anti-sm) that reacts with snrna-binding proteins. fully grown oocytes and embryos prior to gastrulation were found to be relatively depleted of u snrnps in their nuclei and to contain an excess of snrna-binding proteins stored in the cytoplasm. during late blastula-early gastrula, or after microinjection of u snrnas int ... | 1983 | 6186395 |
| a cobalt study of medullary sensory projections from lateral line nerves, associated cutaneous nerves, and the viiith nerve in adult xenopus. | the medullary projections of the anterior lateral line nerve, dorsal branch (alln.d), the posterior lateral line nerve, dorsal branch (plln.d), associated cutaneous nerves, and the viiith nerve in xenopus laevis have been delineated by axonal infusion of cobalt chloride and silver intensification. the peripheral innervation of the posterior lateral line sense organs has also been traced. from wholemount and sectioned preparations, we describe three central projections, extending the length of th ... | 1983 | 6187781 |
| [effects of lindane, an organochlorine insecticide, on the thyroid gland of larvae of xenopus laevis daudin in premetamorphosis]. | the effects of 0.5 ppm of lindane were studied on the morphogenesis and the initial functioning of the thyroid gland. some disturbances were observed: the formation of the first follicles were delayed and ultrastructural changes were noted: increase in the number of mitochondria, reduction of the endoplasmic reticulum. this demonstrates a noxious effect of lindane at the beginning of the functional maturation of the thyroid gland. | 1982 | 6188517 |
| t-lymphocyte and b-lymphocyte dichotomy in anuran amphibians: i. t-lymphocyte proportions, distribution and ontogeny, as measured by e-rosetting, nylon wool adherence, postmetamorphic thymectomy, and non-specific esterase staining. | we used sheep erythrocyte (srbc) e-rosetting, nylon wool fractionation thymectomy and nonspecific esterase staining to assess t-lymphocyte characteristics in rana pipiens during various developmental stages. t-lymphocytes appear in the spleens of premetamorphic tadpoles. we found significant levels of lymphocytes classifiable as t-cells in the peripheral blood of adults, but fewer numbers of t-cells in the thymus, jugular bodies, spleen, pronephros, mesonephros, liver and bone marrow. in additio ... | 1983 | 6188637 |
| estrogen regulates the absolute rate of transcription of the xenopus laevis vitellogenin genes. | estrogen regulates the synthesis of the egg yolk precursor protein, vitellogenin, by causing both a 20-60-fold increase in the absolute rate of total nuclear rna synthesis and a selective increase of at least several thousand fold in the absolute rate of vitellogenin gene transcription. vitellogenin gene transcription is undetectable in unstimulated and withdrawn xenopus laevis liver cells and in cultured xenopus kidney cells allowing us to set a very low upper limit (less than 1 transcript/vite ... | 1983 | 6189836 |
| tandemly repeated dna sequences from xenopus laevis. i. studies on sequence organization and variation in satellite 1 dna (741 base-pair repeat). | a family of tandemly repeated sequences, having a basic repeating unit of 741 base-pairs, has been identified in xenopus laevis dna and designated satellite 1. apart from its rather long repeat unit, the characteristics of this dna appear to be quite similar to those of complex satellite dnas from other organisms. the nucleotide sequence of a cloned repeat unit shows no evidence of simpler internal repeats, and there is no obvious suggestion of reasonable rna- or protein-coding regions. transcri ... | 1983 | 6189999 |
| tandemly repeated dna sequences from xenopus laevis. ii. dispersed clusters of a 388 base-pair repeating unit. | a repetitive dna sequence family from xenopus laevis that has an unusual genomic organization has been identified. it has been shown by blot-hybridization that this sequence occurs in clusters containing variable numbers of the 388 base-pair repeating unit. there are approximately 500 such clusters in the genome, and each cluster has common flanking sequences. the number of tandem 388 base-pair repeats per cluster ranges from one to at least 15, with a mean of seven. homologous sequences were fo ... | 1983 | 6190000 |
| rna synthesis dependence of action potential development in spinal cord neurones. | the role of transcription in the development of electrical properties of neuronal membranes has been largely unexplored. to study the molecular events which result in the expression of these properties it is useful to describe the timing of the underlying rna synthetic events. for example, the timing of the transcription involved in denervation-induced action potentials in frog slow muscle fibres and brain extract-induced sodium channels in chick muscle cells has been investigated. previous stud ... | 1983 | 6190089 |
| effect of 5'-methylthioadenosine on rna and dna synthesis in cultured xenopus laevis cells. | we have examined the effect of 5'-methylthioadenosine (mta) on rna metabolism and dna synthesis in a cultured xenopus laevis epithelial cell line. cells incubated in the presence of mta were transcriptionally less active than controls as measured by the run-off transcription technique. experiments which measured the percentage of newly-synthesized poly(a)+ rna and alpha-amanitin-sensitive nuclear transcripts suggested that mta inhibited transcription by both rna polymerases i and ii. dna synthes ... | 1983 | 6193983 |
| silver positivity of the nors during embryonic development of xenopus laevis. | transcriptional activity of ribosomal rna (rrna) genes is detectable around blastula-gastrula transition during the embryonic development of amphibians and other non-mammalian systems. the silver staining reaction, known to selectively stain transcriptionally active nucleolus organizer regions (nors) both in interphase and metaphase chromosomes allowed us to follow the activation of the nors during the embryonic development of xenopus laevis. | 1983 | 6193984 |
| rna stabilization and continued rna processing following nuclear dissolution in maturing xenopus laevis oocytes. | the xenopus laevis oocyte provides a convenient system for studying cell cycle-induced changes in rna metabolism. initially arrested at first meiotic prophase, it can be induced in vitro to undergo maturation by incubation in the presence of progesterone, progressing to second meiotic metaphase over the course of several hours. the dissolution of the nuclear membrane before the onset of first meiotic metaphase (also known as germinal vesicle breakdown, or gvbd) provides a convenient indication o ... | 1983 | 6194033 |
| the use of monoclonal antibodies for the characterization of a 5 s gene-specific transcription factor (iiia) from xenopus laevis. | monoclonal antibodies were raised against a 5 s gene-specific transcription factor (tfiiia) from xenopus laevis oocytes. seven stable hybridoma lines were established and shown to secrete antibodies directed against different antigenic structures present on distinct peptides of the factor (generated by cleavage of tfiiia with cyanogen bromide). all antibodies react with denatured tfiiia in nitrocellulose blots, but only five are able to bind to the native protein. these antibodies recognize the ... | 1983 | 6194158 |
| intermediate-size filaments in a germ cell: expression of cytokeratins in oocytes and eggs of the frog xenopus. | vitellogenic oocytes and eggs of the frog xenopus laevis contain intermediate-size filaments that are resistant to extractions in high-salt buffers and triton x-100 and are specifically stained with antibodies to cytokeratins. gel electrophoresis of cytoskeletal proteins from xenopus oocytes shows a specific enrichment of three polypeptides designated components 1 [mr, 56,000; iep (pi obtained by two-dimensional gel electrophoresis in the presence of 9.5 m urea), ca. 5.9], 2 (mr, 46,000; iep, 5. ... | 1983 | 6194528 |
| purified rna polymerase iii accurately and efficiently terminates transcription of 5s rna genes. | rna polymerase iii was purified to about 90% homogeneity from ovarian tissue of xenopus laevis. the enzyme accurately initiates and terminates transcription of 5s rna synthesis in isolated nuclei, but not when naked 5s dna is used as a template. a sensitive hybridization technique was used to demonstrate that the purified polymerase, even when supplemented with a transcription factor that binds specifically to the 5s rna gene internal control region, is unable to initiate synthesis at the start ... | 1983 | 6194892 |
| sexual dimorphism in the fibers of a "clasp" muscle of xenopus laevis. | when antibodies specific to fast-twitch, slow-twitch, and slow-tonic myosins were used to stain the clasp muscle, m. sternoradialis, of xenopus laevis, three predominant fiber types were identified in both males and females. three fiber types can also be distinguished by the diameters and conduction velocities of their motor nerves. significant differences in the numbers of slow-tonic fibers were identified between the genders and between control and castrated male animals. this finding suggests ... | 1983 | 6195010 |
| [protein kinase, phosphatase and protease activities in a fraction of rna-binding proteins]. | the rna-binding proteins from amphibian (rana temporaria and xenopus laevis) oocytes contain a camp-independent caseintype protein kinase activity. this enzyme can phosphorylate casein but does not phosphorylate histones. using high voltage paper electrophoresis of acid hydrolysate of [32p]casein, it was found that p-o-phosphoserine and [32p]-o-phosphothreonine are formed via the phosphorylation reaction. protein kinase retains the ability to bind poly(u) under physiological ionic strength value ... | 1983 | 6196057 |
| poly(a) rna of the egg cytoplasm: structural resemblance to the nuclear rna of somatic cells. | this paper concerns the structural characteristics of the poly(a) rna stored in unfertilized amphibian and echinoderm eggs. though located in the egg cytoplasm, at least two-thirds of these maternal transcripts display an interspersed sequence organization similar to that of nuclear rna. in xenopus laevis interspersed poly(a) rna molecules are synthesized and deposited in the oocyte cytoplasm throughout the main growth phase of oogenesis. regions of the sea urchin genome that are represented by ... | 1983 | 6196164 |
| xenopus laevis u2 snrna genes: tandemly repeated transcription units sharing 5' and 3' flanking homology with other rna polymerase ii transcribed genes. | xenopus laevis u2 small nuclear rna (snrna) genes were isolated and expressed by microinjection into frog oocytes. the genes are organised in short tandemly repeated units of approximately 830 bp. some of the cloned tandem repeats are closely linked to genes coding for u5 snrna, trna and an uncharacterised 7s rna. no evidence was found for u2 snrna pseudogenes. single repeat units are transcriptionally active, showing that all the signals necessary for u2 snrna transcription are included in an 8 ... | 1983 | 6196192 |
| a monoclonal antibody against nuclear lamina proteins reveals cell type-specificity in xenopus laevis. | immunofluorescence microscopy shows that the monoclonal murine antibody pkb8 stains the nuclear lamina of various somatic cells from vertebrates as diverse as mammals, birds and amphibia. it also decorates the nuclear periphery of oocytes from rat and chicken but does not react with spermatocytes, spermatids and spermatozoa. immunoblotting experiments demonstrate reaction with lamina polypeptides a, b and c of rat, with lamina polypeptide a of chicken, and with lamina polypeptides li and lii of ... | 1984 | 6198191 |
| oscillatory motion of intra-axonal organelles of xenopus laevis following inhibition of their rapid transport. | the motion of optically detected organelles in myelinated axons of xenopus laevis was studied in axons bathed in a potassium glutamate based medium and in axons in a similar medium to which various inhibitors of axonal transport were added. organelles in the potassium glutamate medium had a motion which was indistinguishable from that previously described for organelles in axons bathed in a conventional physiological saline. colchicine, dimethylsulphoxide, 2,4-dinitrophenol, hyperosmotic solutio ... | 1983 | 6198513 |
| interferon activity produced by interferon messenger rna in tilapiamosaiabica peters oocytes. | the activities of interferon mrna from various types of mouse cells have been studied using tilapiamosaiabica peters oocytes (tpo) as the translation system. the translation activity of interferon mrna in tpo was also compared with that in xenopus laevis oocytes (xlo). the results obtained showed similar translation efficiency in both systems. the highest translation efficiency was observed when t. peters oocytes, microinjected with mrna, were cultivated in eagle's medium containing 0.01% hepes ... | 1983 | 6198582 |
| contribution of maternal mrna for maintenance of ca2+-dependent reaggregating activity in dissociated cells of xenopus laevis embryos. | dissociated xenopus laevis blastula cells, where reaggregation was inhibited in ca2+-free medium, reaggregated immediately after the addition of ca2+. this reaggregation was not inhibited by cordycepin or actinomycin d treatment during culture, although cycloheximide and puromycin were inhibitory. the reaggregation was not inhibited even when fertilized eggs were microinjected with cordycepin and their rna synthesis was continuously inhibited through cleavage to blastula stages. in neurula cells ... | 1983 | 6199118 |
| sequence homologies within the 5' end region of the estrogen-controlled vitellogenin gene in xenopus and chicken. | in oviparous vertebrates vitellogenin, the precursor of the major yolk proteins, is synthesized in the liver of mature females under the control of estrogen. we have established the organization and primary structure of the 5' end region of the xenopus laevis vitellogenin a2 gene and of the major chicken vitellogenin gene. the first three homologous exons have exactly the same length in both species, namely 53, 21 and 152 nucleotides, and present an overall sequence homology of 60%. in both spec ... | 1983 | 6199194 |
| a temporal variation in nonneuronal protein synthesis in dorsal root ganglia and nerve and its significance to studies of axonal transport. | protein synthesis and fast axonal transport were studied in vitro using dorsal root ganglia (drg)-sciatic nerve preparations from the amphibian xenopus laevis. it was observed that the rate of incorporation of [3h]leucine into protein in drg and isolated segments of nerve began to increase 9 to 11 h after killing the animal, attaining at 13 to 17 h a maximum of 5- to 10-times preincrease (less than 9 h) values. at the same time as an increase in the rate of incorporation began, synthesis commenc ... | 1984 | 6199227 |
| cell lineage analysis of neural induction: origins of cells forming the induced nervous system. | horseradish peroxidase (hrp) was used as an intracellular lineage tracer in two experiments designed to reveal the sites of origin of cells that formed the duplicate embryo which developed in relation to an organizer grafted in the ventral marginal zone (vmz) of xenopus laevis embryos. in the first experiment a dorsal blastoporal lip fully labeled with hrp was grafted in the vmz of an unlabeled embryo at the beginning of gastrulation. this resulted in development of a second embryo in which labe ... | 1984 | 6199240 |
| in vitro methylation of hpaii sites in xenopus laevis rdna does not affect its transcription in oocytes. | the effect of methylation of x. laevis rdna on its transcription was tested by methylating all of the hpaii sites in a series of rdna plasmids and injecting the methylated rdna into x. borealis oocytes. analysis of rna transcribed from the injected plasmids showed that methylation of rdna in vitro does not affect transcription of x. laevis ribosomal genes. this result suggests that despite the observed correlation between demethylation of rdna and synthesis of ribosomal rna in x. laevis embryos ... | 1984 | 6199746 |
| enrichment of the poly (a) sequence and lack of enhancement of total rna synthesis in cultured xenopus hepatocytes by estradiol-17 beta. | the effect of estradiol-17 beta on rna synthesis and the amounts of total rna and polyadenylic acid were determined in primary cultures of xenopus laevis liver parenchymal cells. results showed that estradiol did not alter the rna content significantly; control cells contained 11.9 +/- 0.34 micrograms and estradiol-treated cells 12.4 +/- 0.17 micrograms per 10(6) cells on day 2 of estradiol treatment, and 22.0 +/- 0.61 micrograms and 24.0 +/- 1.09 micrograms on day 5. hybridization with [3h]poly ... | 1983 | 6200239 |
| cyclosporin a is a differential inhibitor of eukaryotic rna polymerases. | in order to investigate the molecular mechanism of biological action of the drug cyclosporin a (csa), we have studied its effect on eukaryotic rna polymerase activities in two systems: (a) in vitro transcription; (b) injection into frog oocytes. the electron microscopic transcription r-loop method [1] has been used to assay for specific transcription of an immunoglobulin gene clone in hela cell lysates. in this system, csa inhibits efficiently the transcription of immunoglobulin genes. dilution ... | 1984 | 6200340 |
| helper activity for antibody synthesis encoded by mrna extracted from human peripheral blood mononuclear cells. | translation products in xenopus laevis of mrna from human peripheral blood mononuclear cells were tested for their capacity to replace t cells in the anti-srbc response of nude spleen cells. when the starting material came from pha or fcs-stimulated lymphocytes, the translated lymphokines, displaying such a b cell helper activity were found to be encoded by mrna sedimenting at 6-7s and 13s on a sucrose density gradient. 6-7s mrna from control, non-stimulated lymphocytes was also able to code for ... | 1984 | 6201168 |
| effects of cordycepin on the synthesis of nuclear and cytoplasmic rnas in embryonic cells of xenopus laevis. | effects of cordycepin on the incorporation of [3h] guanosine into embryonic xenopus cells were examined. cordycepin inhibited the labeling not only of poly(a) + rna, but of all the other major classes of rnas. cellular fractionation showed that this inhibition was much stronger in the labeling of cytoplasmic rnas than of nuclear rnas. [3h]cordycepin was incorporated into both poly(a) + rna and other rna species. | 1983 | 6201296 |
| coincidence of endoplasmic reticulum pattern as visualized by fitc-con a-fluorescence and electron microscopy. | fitc-con a-fluorescence and electron microscopy have been used in parallel for the visualization of rough endoplasmic reticulum in xenopus laevis tadpole heart primary tissue culture cells. rer distribution pattern as revealed by both methods is compared by superimposition of images of the same cell. coincidence of rer distribution is established. | 1984 | 6201466 |
| ultrastructural localization of nucleolar organizers during oogenesis in xenopus laevis using a silver technique. | silver staining at the electron microscopic level of the nucleolar organizers was carried out on xenopus laevis oocytes at various stages of oogenesis. the results indicate that a positive reaction takes place exclusively in the dense fibrillar component of the extrachromosomal nucleoli. this constituent undergoes morphological changes of distribution and architecture, which have been correlated with modifications of the transcriptional activity of the nucleoli. when nucleolar activity is reduce ... | 1984 | 6201496 |
| sensory physiology, anatomy and immunohistochemistry of rohon-beard neurones in embryos of xenopus laevis. | rohon-beard neurones show substance p-like immunoactivity in their somas and in their centrally projecting axons. peripherally, the morphology of their free nerve endings within the trunk skin has been shown using horseradish peroxidase staining. the excitation of rohon-beard neurones by natural and electrical stimulation of the skin has been examined using intracellular micro-electrodes in the late embryo of xenopus laevis. rohon-beard cells are sensitive to transient, local indentation of the ... | 1984 | 6201612 |
| studies on xenopus immunoglobulins using monoclonal antibodies. | monoclonal antibodies raised against xenopus ig recognize antigenic determinants on igm and low mol. wt ig (lmw ig or igy ). on sds-page two forms of mu were distinguished in the supernatant and cell lysate of tunicamycin-treated spleen cell culture. the two bands of v observed in serum appear to be the result of carbohydrate heterogeneity. the light chains resolved into two distinct bands which differed in peptide maps; the more slowly migrating band of light chain was preferentially associated ... | 1984 | 6203031 |
| xenopus laevis u1 snrna genes: characterisation of transcriptionally active genes reveals major and minor repeated gene families. | xenopus laevis u1 snrna genes are found in several different genomic arrangements. the major family of genes is organised in tandem repeats of 1.8 kb. the minor u1-family is much less abundant and is present on 1.2-kb hinfi restriction fragments. in addition there are genomic arrangements present in one or very few copies, which could represent the ends of repeating units. there is no evidence for the presence of u1 pseudogenes in xenopus. a cluster of u1 snrna genes consisting of a member of th ... | 1984 | 6203742 |
| immunological identity of proteins that bind stored 5s rna in xenopus oocytes. | in small oocytes of xenopus laevis, the three most abundant proteins are isolated as basic polypeptides with molecular weights of 48 kd (p48), 43 kd (p43) and 40 kd (p40, also known as transcription factor iiia). all three proteins share common properties in being able to bind specifically ribosomal 5s rna molecules and influence, in different ways, their rates of production and utilization. it has been shown by biochemical analysis and immunological characterization that the three proteins are ... | 1984 | 6203770 |
| early cellular interactions promote embryonic axis formation in xenopus laevis. | we have attempted to define the location and mode of action of axial determinants in the egg of xenopus laevis. to this end, we transplanted small numbers of blastomeres from normal 64-cell stage embryos into synchronous recipient embryos which had been irradiated with ultraviolet light prior to first cleavage. without transplantation, such embryos fail to develop dorsal structures of the embryonic body axis. we found that one to three blastomeres transplanted from the vegetal-most octet of cell ... | 1984 | 6203792 |
| synthesis of human u1 rna. ii. identification of two regions of the promoter essential for transcription initiation at position +1. | we have analyzed the requirements for human u1 rna transcription catalyzed by rna polymerase ii. in xenopus laevis oocytes, a human u1 rna gene with only 231 and 35 nucleotides of the 5' and 3' flanking regions, respectively (lund, e. and dahlberg, j. e. (1984) j. biol. chem. 259, 2013-2021), is able to support accumulation of human u1 rna. we show that the point in the template corresponding to the 5' end of u1 rna is a site of transcription initiation. that result rules out the possibility tha ... | 1984 | 6203910 |
| amino acid sequence of the carboxy-terminal part of an acidic type i cytokeratin of molecular weight 51 000 from xenopus laevis epidermis as predicted from the cdna sequence. | the dna sequence of a clone from a cdna library made from xenopus laevis skin is described. this sequence represents the 3'-terminal end of an mrna which codes for an epidermal cytokeratin polypeptide of mol. wt. 51 000 of the acidic (type i) subfamily as identified by hybridization-selection of mrnas, followed by gel electrophoretic identification of the polypeptides synthesized by translation in vitro. the partial amino acid sequence of the amphibian cytokeratin shows strong similarity to type ... | 1984 | 6204859 |
| the histone h5 variant in xenopus laevis. | the presumptive histone h5 of xenopus laevis has been characterized by sds and acid-urea-triton polyacrylamide gel electrophoresis and compared with chicken histone h5. chicken h5 has a lower electrophoretic mobility compared to that of xenopus h5 in both gel systems. it is shown, using a polyclonal antiserum against chicken h5, that the xenopus histone h5 is immunologically related to chicken histone h5. monoclonal antibodies have been prepared to the xenopus histone types h5 and h1a, that do n ... | 1984 | 6205766 |
| topography of the retinal ganglion cell layer of xenopus. | cell distribution in the retinal ganglion cell layer of xenopus laevis was studied by electron microscopy and the retinal wholemount method. unlike the familiar stratification of the retina, the ganglion cell perikarya and their axons were localised in the same layer, but strictly segregated in alternate rows converging in a radial pattern on the optic disc. rows of perikarya (retinal cords) were two to ten cells wide and clearly defined for a little more than half the distance between the optic ... | 1984 | 6206043 |
| altered levels of a 5 s gene-specific transcription factor (tfiiia) during oogenesis and embryonic development of xenopus laevis. | xenopus laevis oocytes contain a 38,000-da protein which serves both as a 5 s gene-specific transcription initiation factor (tfiiia) and to stabilize 5 s rna in ribonucleoprotein complexes. using an antibody to this protein we have measured the levels of tfiiia during oogenesis and embryonic development in x. laevis. the maximal steady state level (approximately 10(12) molecules/oocyte) is reached early in oogenesis but drops 10- to 20-fold in later stages and another 10- to 20-fold during ovula ... | 1984 | 6206067 |
| patterns of junctional communication in the early amphibian embryo. | it has long been recognized that cells in early embryos can communicate with each other via a direct cell-to-cell pathway, probably mediated by gap junctions. low electrical resistance pathways, detected electrophysiologically, have been identified in all species examined so far. however, studies in various embryos on the transfer of molecules larger than small ions (for example, fluorescent dyes in the molecular weight range 350-500) have given conflicting results. in all these studies the abil ... | 1984 | 6206399 |
| transcription of a long, interspersed, highly repeated dna element in xenopus laevis. | we have analyzed the transcription of 1723, a long, repeated dna element that is interspersed in the genome of xenopus laevis (b. k. kay and i. b. dawid (1983) j. mol. biol. 170, 583-596). we have detected rna homologous to 1723 in total cellular rna from ovaries, embryos, liver, and cultured kidney cells. transcripts from both strands of the element are present at similar concentrations in these different rna preparations. in oocytes, approximately 100 pairs of lampbrush chromosome loops are ac ... | 1984 | 6207063 |
| differential expression of multiple u1 small nuclear rnas in oocytes and embryos of xenopus laevis. | the small nuclear rna, u1, is a highly conserved, 165 nucleotide long rna which has been implicated in the processing of mrna precursors. we present evidence that in the amphibian x. laevis there exist at least seven species of u1 rna, which differ in sequence but not in length. strikingly, these rnas are not coordinately expressed. two of the u1 rnas are the predominant u1 species transcribed in the late blastula-early gastrula stages of xenopus embryogenesis. these two rnas, designated xu1a an ... | 1984 | 6207932 |
| small nuclear u-ribonucleoproteins in xenopus laevis development. uncoupled accumulation of the protein and rna components. | the accumulation of protein and rna components of small nuclear u-ribonucleoprotein particles is non-co-ordinate during oogenesis and early embryogenesis in xenopus laevis. northern blot hybridization of a cloned xenopus u2-rna gene to oocyte and embryo rnas demonstrates that the amount of small nuclear u2-rna per oocyte reaches a plateau early in oogenesis (at the start of yolk deposition); further accumulation is not observed in oogenesis, nor in embryogenesis until the late blastula stage. in ... | 1984 | 6208365 |
| multiple ubiquitin mrnas during xenopus laevis development contain tandem repeats of the 76 amino acid coding sequence. | a cdna clone, pxlgc20, was isolated from a library constructed from poly(a)+ rna from stage 10 x. laevis gastrulae. this sequence hybridizes with up to nine different rna species ranging in size from 1600 to 3500 nucleotides, regularly spaced at intervals of about 230 nucleotides. clone pxlgc20 contains two complete repeats of a 228 bp sequence as well as part of a third repeat, all adjacent and in the same orientation. one possible translational reading frame in pxlgc20 completely spans the rep ... | 1984 | 6209017 |
| alu sequences are processed 7sl rna genes. | 7sl rna is an abundant cytoplasmic rna which functions in protein secretion as a component of the signal recognition particle. alu sequences are the most abundant family of human and rodent middle repetitive dna sequences (reviewed in ref. 2). the primary structure of human 7sl rna consists of an alu sequence interrupted by a 155-base pair (bp) sequence that is unique to 7sl rna. in order to obtain information about the evolution of the alu domain of 7sl rna, we have determined the nucleotide se ... | 1984 | 6209580 |
| 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 |
| [electrophoresis of native cardiac myosin in anura amphibians]. | electrophoresis in non dissociating conditions of native cardiac myosin was adapted to the study of amphibian myosin. utilization of potassium ion has allowed to obtain a good separation of myosin isoenzymes. an evolution of isoenzymic composition of cardiac myosin during metamorphosis and aging in xenopus laevis (daudin) was observed. | 1983 | 6221780 |
| high mobility group proteins of amphibian oocytes: a large storage pool of a soluble high mobility group-1-like protein and involvement in transcriptional events. | oocytes of several amphibian species (xenopus laevis, rana temporaria, and pleurodeles waltlii) contained a relatively large pool of nonchromatin-bound, soluble high mobility group (hmg) protein with properties similar to those of calf thymus proteins hmg-1 and hmg-2 (protein hmg-a; a, amphibian). about half of this soluble hmg-a was located in the nuclear sap, the other half was recovered in enucleated ooplasms. this protein was identified by its mobility on one- and two-dimensional gel electro ... | 1983 | 6224801 |
| tumor promoter tpa increases initiation of replication on dna injected into xenopus eggs. | the effect of the tumor promoter tpa on the control of dna replication was assayed by following the regulated replication of dna microinjected into eggs of the frog xenopus laevis. tpa increases the amount of replication of injected dna. both initiation of replication on parental dna molecules and reinitiation on previously replicated molecules are stimulated. interaction with the external membrane appears necessary since injections of high concentrations of tpa into the egg are ineffective, whe ... | 1983 | 6226366 |
| aggregates of acetylcholine receptors are associated with plaques of a basal lamina heparan sulfate proteoglycan on the surface of skeletal muscle fibers. | hybridoma techniques have been used to generate monoclonal antibodies to an antigen concentrated in the basal lamina at the xenopus laevis neuromuscular junction. the antibodies selectively precipitate a high molecular weight heparan sulfate proteoglycan from conditioned medium of muscle cultures grown in the presence of [35s]methionine or [35s]sulfate. electron microscope autoradiography of adult x. laevis muscle fibers exposed to 125i-labeled antibody confirms that the antigen is localized wit ... | 1983 | 6226669 |
| genetic recombination of bacteriophage lambda dnas in xenopus oocytes. | pairs of genetically marked bacteriophage lambda dnas have been injected into xenopus laevis oocyte nuclei. after suitable incubation, dna was recovered and packaged into phage particles in vitro. when these were plated onto a selective host, phage recombinant for parental markers were observed. recombination was dependent on both parents being present in the same oocyte nucleus and was roughly proportional to the physical separation of the markers. thus, the oocytes appear to contain the machin ... | 1983 | 6227916 |
| lectins and substitution for helper function in anti-hapten responses in xenopus laevis. | substitution by lectins for the carrier-priming requirement in thymus-dependent, antigen-binding responses in xenopus laevis has been examined. concanavalin a (con a) was found to substitute for carrier priming in control, early-thymectomized and adult-thymectomized animals, but not in animals given a single, high dose of n-methyl-n-nitrosourea, which has a permanent effect on certain thymus-dependent functions in this species. lipopolysaccharide and other lectins, such as peanut agglutinin and ... | 1984 | 6235180 |
| [expression of hepatitis b virus (hbv) genome in the oocytes of two species of amphibians]. | xenopus laevis and pleurodeles waltlii oocyte nuclei are injected with a recombinant plasmid pcp 10, carrying two hepatitis b virus (hbv) genomes in a tandem arrangement. transcription occurs in oocytes of both species and production of viral rnas is demonstrated; better quantitative results are obtained with p. waltlii oocytes. two viral proteins are detected: hepatitis b surface antigen (ag hbs) and hepatitis b core antigen (ag hbc). these proteins can be shown only in oocyte homogenates, and ... | 1984 | 6235876 |
| cell surface expression of murine, rat, and human fc receptors by xenopus oocytes. | we report that xenopus laevis oocytes can efficiently translate and insert heterologous membrane receptors into the oocyte plasma membrane, where they can be detected by the binding of either monoclonal antibodies or ligands. thus, oocytes injected with mrna from the mouse j774 macrophage-like cell line, the rat rbl-1 basophilic leukemia, and the u937 promonocyte cell line, bound 2.4g2 fab, rat ige, and mouse igg2a, respectively. the increase in the high avidity fc gamma r observed after gamma-i ... | 1984 | 6236275 |
| a qualitative difference in the interleukin 2 (il-2) requirement of helper and cytotoxic t lymphocytes. | a qualitative difference in the requirement of mouse helper and cytotoxic t lymphocytes for interleukin 2 (il-2) was revealed by offering such cells il-2 synthesized in xenopus laevis oocytes that had been microinjected with messenger rna (mrna) encoding human il-2. while both helper and cytotoxic mouse t-cell lines proliferate in response to the il-2 present in medium conditioned by stimulated human lymphocytes, only helper-t-cell lines respond to human il-2 secreted from oocytes. this result d ... | 1984 | 6236885 |
| calcium sequestering activities of reticulum vesicles from xenopus laevis oocytes. | membrane vesicles isolated from xenopus laevis full-grown stage vi and mature oocytes accumulate 45ca in the presence of atp and oxalate. the ca2+-pumping activity measured in vitro does not appear to be modified during meiotic maturation; it is not affected by the complex ca2+-calmodulin. preliminary experiments have shown that the addition of na+ (30 mm) rapidly discharges accumulated 45ca into oocyte vesicles indicating that a na+/ca2+ exchange system occurs in this membrane fraction. during ... | 1984 | 6238836 |
| localization of soluble endogenous lectins and their ligands at specific extracellular sites. | soluble lectins of chicken, rat, frog, and the cellular slime mold, dictyostelium discoideum, were purified and specific antibodies raised against these proteins were used to immunohistochemically localize the lectins in and around the tissues in which they were synthesized. within cells, some of these soluble lectins (chicken-lactose-lectin-ii in intestinal goblet cells, discoidin ii in prespore cells) appear to be concentrated within vesicles whereas others (e.g., rat beta-galactoside lectin i ... | 1984 | 6240298 |
| type ii dna topoisomerases: enzymes that can unknot a topologically knotted dna molecule via a reversible double-strand break. | the t4 dna topoisomerase is a recently discovered multisubunit protein that appears to have an essential role in the initiation of t4 bacteriophage dnd replication. treatment of double-stranded circular dna with large amounts of this topoisomerase in the absence of atp yields new dna species which are knotted topological isomers of the double-stranded dna circle. these knotted dna circles, whether covalently closed or nicked, are converted to unknotted circles by treatment with trace amounts of ... | 1980 | 6244895 |
| phylogenetic distribution of [3h]kainic acid receptor binding sites in neuronal tissue. | the phylogenetic distribution of specific binding sites for kainic acid was determined in 14 species including invertebrates and vertebrates. the highest level of binding was observed in brains of the frog (xenopus laevis), followed by the spiny dogfish (heterodontus francisci), the goldfish (carasius auratus) and the chick (gallus domesticus). although significant specific binding was noted in some of the lowest forms tested (e.g. hydra littoralis), this was not a consistent observation in the ... | 1980 | 6247025 |
| modulation of transcription from chromatin assembled in vitro. | a small plasmid dna was assembled into chromatin in vitro by incubation in an extract prepared frog eggs of xenopus laevis. the plasmid dna contrained the regulatory region of the escherichia coli lac operon, the transcription of which is under positive regulation by catabolite activator protein (cap) and negative regulation by lac repressor. after incubation in the egg extract the plasmid dna acquired approximately 60% of the predicted maximum number of nucleosomes. chromatin was treated with p ... | 1980 | 6249342 |
| distribution of sequences common to the 25--28s-ribonucleic acid genes of xenopus laevis and neurospora crassa. | the extent of homology between the nucleotide sequence of l-rrna (the major rna component of the larger ribosomal subparticle) of a lower eukaryote (neurospora crassa) and an amphibian (xenopus laevis) was investigated by utilizing rdna (dna coding for rrna) of x. laevis cloned in plasmids pmb9 and pml2, and rdna of n. crassa cloned in bacteriophage lambda. hybridization studies revealed that sequences common to both n. crassa and x. laevis l-rrna comprise a total of approx. 1050 /+- 200 nucleot ... | 1980 | 6250536 |
| polyethylene glycol- and lysolecithin-induced cell fusion between follicle cell and very small oocyte in xenopus laevis. | | 1980 | 6250867 |
| studies of microbial toxins in xenopus laevis oocytes. | | 1980 | 6253305 |
| cyclic amp phosphodiesterase activities in xenopus laevis oocytes. | cyclic amp phosphodiesterase activity has been identified in full-grown xenopus oocytes in vivo and in vitro. about 50% of the in vitro phosphodiesterase activity was present in the solution fraction and 35% in a partially purified membrane fraction. both activities exhibited high substrate affinity (km about 10(-6) m). sucrose gradient fractionation revealed two forms of phosphodiesterase: a 5 s form (peak i) and a 6.5 s form (peak ii). treatment with trypsin led to the activation of the solubl ... | 1980 | 6253341 |
| nucleotide sequence encoding the 5' end of xenopus laevis 18s rrna. | we have sequenced a region of cloned xenopus laevis ribosomal dna encompassing the last 24 nucleotides of the external transcribed spacer and the first 275 nucleotides of the 18s gene. the start of the 18s gene was identified by correlating the results obtained from rna hybridization and fingerprinting with the dna sequence. this 5' region of 18s rrna contains five 2'-o-methyl groups and at least six pseudouridine residues. several of these modified nucleotides are clustered into a relatively sh ... | 1980 | 6253895 |
| the 10 kb drosophila virilis 28s rdna intervening sequence is flanked by a direct repeat of 14 base pairs of coding sequence. | most repeat units of rdna in drosophila virilis are interrupted in the 28s rrna coding region by an intervening sequence about 10 kb in length; uninterrupted repeats have a length of about 11 kb. we have sequenced the coding/intervening sequence junctions and flanking regions in two independent clones of interrupted rdna, and the corresponding 28s rrna coding region in a clone of uninterrupted rdna. the intervening sequence is terminated at both ends by a direct repeat of a fourteen nucleotide s ... | 1980 | 6253902 |
| organization of 5s genes in chromatin of xenopus laevis. | the chromatin organization of the genes coding for 5s rna in xenopus laevis has been investigated with restriction endonucleases and micrococcal nuclease. digestion of nuclei from liver, kidney, blood and kidney cells maintained in culture with micrococcal nuclease reveals that these xenopus cells and tissues have shorter nucleosome repeat lengths than the corresponding cells and tissues from other higher organisms. 5s genes are organized in nucleosomes with repeat lengths similar to those of th ... | 1980 | 6253929 |
| cloning of an origin of dna replication of xenopus laevis. | dna fragments of xenopus laevis, the african frog, were cloned in the ecori site of the escherichia coli plasmid pacyc189 and tested for ability to initiate and complete replication of the recombinant plasmid when injected into unfertilized eggs of x. laevis. after measurement of the [3h]-thymidine incorporation per egg for a number of recombinant plasmids, psw14 and psw9, which respectively contain a small segment (550 base pairs) and several kilobases of frog dna, were selected for more extens ... | 1980 | 6254072 |
| regulated replication of dna microinjected into eggs of xenopus laevis. | purified circular dna of sv40 or polyoma virus has been injected into unfertilized eggs of xenopus laevis. injected dna initiates and completes multiple rounds of semiconservative replication while observing cellular regulatory signals. thus replication initiation of double-stranded templates is induced after the oocyte is matured in vitro by progesterone. only one round of replication of injected dna is observed in a single cell cycle. when protein synthesis is inhibited unreplicated molecules ... | 1980 | 6254667 |
| histone genes from xenopus laevis: molecular cloning and initial characterization. | histone dna sequences, were detected in eco ri fragments of total xenopus laevis dna, by hybridization with 32p-labeled h22-dna, a histone gene repeat unit of the sea urchin psammechinus miliaris. the about 6 kb-size class, which was found to hybridize, was subsequently integrated into the e. coli plasmid pcr1. a clone was isolated that contains a 5.8 kb ecori fragment hybridizing with h22-dna. a physical map was constructed using the restriction endonucleases bamhi, psti, hincii, bglii, xbai, p ... | 1980 | 6254837 |
| recombination of a eukaryotic dna in bacteria. | single, 824 bp repeating units of xenopus laevis oocyte-type 5s dna were inserted into the recombination vectors, lambda rva and lambda rvb. when the inserts had the same orientation with respect to the lambda chromosomes. spi- imm434 recombinants were recovered by selection on a p2, lambda double lysogenic host. because of the structure of the vectors, the crossover point in each recombinant must lie completely within the 5s dna insert. the physical characteristics of these recombinants were de ... | 1980 | 6254845 |
| characterization of cloned complementary dna covering more than 6000 nucleotides (97%) of avian vitellogenin mrna. | the messenger rna coding for chicken vitellogenin, a precursor of the egg-yolk proteins lipovitellin and phosvitin, is synthesized in the liver following estrogen injection. this mrna is 6600 nucleotides long. we have previously reported the cloning and preliminary characterization of some cdna fragments representing portions of the vitellogenin mrna [biochem. biophys. acta, 606, 34--46 (1980)]. in this paper we report the full characterization of a larger series of such clones, representing alm ... | 1980 | 6257510 |
| the emergence, localization, and maturation of neurotransmitter systems during development of the retina in xenopus laevis: ii. glycine. | the high-affinity uptake and release of glycine was studied in retinas of xenopus laevis. in the toad and tadpole retina, 3h-glycine was accumulated by a population of cells located predominantly in the inner nuclear layer. when retinas preloaded with 3h-glycine were subjected to high k+-concentrations, these retinas released large amounts of 3h-glycine by a ca++-dependent mechanism. the appearance and maturation of these putative glycinergic properties was followed during retinal development. o ... | 1981 | 6257765 |
| the emergence, localization, and maturation of neurotransmitter systems during development of the retina in xenopus laevis. iii. dopamine. | the uptake, synthesis, and release of dopamine was studied in retinas of xenopus laevis. in the tadpole and adult retina, 3h-dopamine is accumulated by cells located in the inner nuclear layer. retinas preloaded with 3h-dopamine release this compound in response to high k+ concentrations in the medium. this release is probably ca++-dependent as it is inhibited by co++ in the medium. adult retinas are also capable of synthesizing 3h-dopamine from 3h-tyrosine. the appearance and maturation of thes ... | 1981 | 6257766 |
| the transcription termination site of the ribosomal rna operon in yeast. | the site at which transcription of the ribosomal rna operon in yeast is terminated was precisely localized. first, the exact position of the 3' end of the 26s rrna gene was mapped on the rdna on the basis of rna- and dna sequence data. next, the 3' terminus of the primary transcript, 37s precursor rrna, was established by hybridization experiments and sequence analysis. 37s pre-rrna appears to be just 7 nucleotides longer at its 3' end than 26s rrna. the non-coding strand around the termination ... | 1980 | 6258138 |
| expression of the herpes thymidine kinase gene in xenopus laevis oocytes: an assay for the study of deletion mutants constructed in vitro. | when xenopus laevis oocyte nuclei are injected with a recombinant plasmid containing the herpes simplex virus (hsv) thymidine kinase (tk) gene, a 100-fold increase in tk enzymatic activity is observed. three lines of evidence show that this increase in tk activity is a result of the expression of the hsv tk gene. first, the enzymatic activity is selectively inactivated by the igg fraction of antiserum raised against hsv tk protein. second, a polypeptide that comigrates with authentic hsv tk on p ... | 1980 | 6258155 |
| nucleotide sequence through the 18s-28s intergene region of a vertebrate ribosomal transcription unit. | we have determined the nucleotide sequence of part of a cloned ribosomal transcription unit from xenopus laevis extending from the 3' region of the 18s gene through the 18s-28s intergene region into the start of the 28s gene. the 18s 3' region possess two tracts of high homology with the corresponding segments of other eukaryotic 18s genes (yeast and bombyx mori) separated by a tract of low homology which in x. laevis is rich in g plus c. the first internal transcribed spacer, between the 18s an ... | 1980 | 6258158 |
| equilibrium properties of a voltage-dependent junctional conductance. | the conductance of junctions between amphibian blastomeres is strongly voltage dependent. isolated pairs of blastomeres from embryos of ambystoma mexicanum, xenopus laevis, and rana pipiens were voltage clamped, and junctional current was measured during transjunctional voltage steps. the steady-state junctional conductance decreases as a steep function of transjunctional voltage of either polarity. a voltage-insensitive conductance less than 5% of the maximum remains at large transjunctional vo ... | 1981 | 6259274 |
| hormone effects on transport in cultured epithelia with high electrical resistance. | three continuous lines of amphibian epithelial cells form epithelia with a high transepithelial resistance (greater than 4,000 omega . cm2) in culture. the cell lines are tb-m and tb-6c, derived from the urinary bladder of bufo marinus, and a6, derived from the kidney of xenopus laevis. short-circuit current is equivalent to net mucosa-to-serosa sodium transport in two cell lines and slightly exceeds sodium transport in epithelia formed by tb-6c cells. none of the cell lines has an adenylate cyc ... | 1981 | 6259946 |
| purification and characterization of xenopus laevis type i topoisomerase. | a topoisomerase activity was purified from mature ovaries and from nuclei of stage 6 oocytes of xenopus laevis. from both preparations we obtained a single polypeptide chain having an estimated molecular weight of 67,000. the enzyme purified from ovaries is active in the presence of 150 mm monovalent cation, but its activity is more than 1 order of magnitude higher in the presence of 6 mm mg2+; the enzyme purified from nuclei requires mg2+ through all the steps of purification. enucleated oocyte ... | 1981 | 6260773 |