| a monoclonal antibody specific for an epidermal cell antigen of xenopus laevis: electron microscopic observations using a gold-labeling method. | a monoclonal antibody (epi-1), raised against the supernatant of a homogenate of xenopus laevis larvae at the tailbud stage (stage 36/37), interacts specifically with a 250 kd epidermal antigen of xenopus. an immunocytochemical gold-labeling technique was used to investigate changes in antigen distribution during epidermal development of xenopus laevis. specific immunolabeling was initially detected over the endoplasmic reticulum in the outer epithelial cells of the late gastrula stage (stage 12 ... | 1988 | 3356895 |
| nucleotide sequence determination and secondary structure of xenopus u3 snrna. | using a combination of rna sequencing and construction of cdna clones followed by dna sequencing, we have determined the primary nucleotide sequence of u3 snrna in xenopus laevis and xenopus borealis. this molecule has a length of 219 nucleotides. alignment of the xenopus sequences with u3 snrna sequences from other organisms reveals three evolutionarily conserved blocks. we have probed the secondary structure of u3 snrna in intact xenopus laevis nuclei using single-strand specific chemical reag ... | 1988 | 3357768 |
| a comparison of the solution structures and conformational properties of the somatic and oocyte 5s rrnas of xenopus laevis. | the secondary and tertiary structures of xenopus oocyte and somatic 5s rrnas were investigated using chemical and enzymatic probes. the accessibility of both rnas towards single-strand specific nucleases (t1, t2, a and s1) and a helix-specific ribonuclease from cobra venom (rnase v1) was determined. the reactivity of nucleobase n7, n3 and n1 positions towards chemical probes was investigated under native (5 mm mgcl2, 100 mm kcl, 20 degrees c) and semi-denaturing (1 mm edta, 20 degrees c) conditi ... | 1988 | 3357778 |
| structural analysis of the mitotic cycle in pre-gastrula xenopus embryos. | the long-known phenomenon of karyomere (chromosome vesicle) formation at early telophase of the nuclear cycle during early embryogenesis of a wide range of organisms including amphibians (rubaschkin 1905; for review, see richards 1917) was investigated in the early cleavage cycles of xenopus laevis embryos before the mid blastula transition. embryos were fixed and epon embedded at successive time intervals and consecutive thick (3 micron) and ultrathin sections cut. using conventional light micr ... | 1988 | 3359878 |
| characterization by human antibodies of two hela cell proteins which are related to xenopus laevis transcription factor tfiiia. | the sera of two patients with autoimmune disorders recognize in hela cell extracts two proteins with apparent molecular masses of 37,000 (p37) daltons and 32,000 daltons (p32). these proteins are non covalently associated with 5s rna and sediment as 7-10 s particles in sucrose density gradients. both proteins are antigenetically related to tfiiia, a previously described protein of xenopus laevis, which is known as a 5s rna transcription factor and occurs in oocytes as a noncovalent complex with ... | 1988 | 3362672 |
| comparison of murine band 3 protein-mediated cl- transport as measured in mouse red blood cells and in oocytes of xenopus laevis. | murine band 3 protein was expressed in oocytes of xenopus laevis after microinjection of the mrna from the spleens of anemic mice. the 36cl- efflux from the oocytes was compared with the chloride fluxes measured in murine red cells. in both oocytes and red cells, the band 3-mediated chloride transport showed the following features: the selective inhibitor of band 3-mediated anion transport, 4,4'-dinitrostilbene-2,2'-disulfonate exerts its effects only when applied to the outside and not when app ... | 1988 | 3365428 |
| structural basis for autogenous regulation of xenopus laevis ribosomal protein l1 synthesis at the splicing level. | it is known that the injection of the xenopus laevis ribosomal protein l1 gene into oocytes causes the accumulation of immature l1 transcripts due to a specific block of splicing of the second and third introns. in this paper the secondary structures of these introns in pre-mrna have been constructed. it has been shown that they share homology with 28 s rrna. the putative rna-binding segment of l1 has also been predicted. these results are interpreted as the structural basis for autogenous regul ... | 1988 | 3366251 |
| interaction of trna transcription factors with satellite i dna from xenopus laevis. | a cloned repeat of xenopus laevis satellite i dna was tested for the ability to form stable complexes with trna transcription factors in vitro. in template exclusion studies, the satellite i dna competed efficiently with a trna gene for binding of yeast rna polymerase iii transcription factors. dnase i footprinting further showed that transcription factor tf iiic alone bound to satellite i dna at both the a block and b block consensus promoter sequences immediately downstream from the transcript ... | 1988 | 3366384 |
| xenopus tadpole melanophores are controlled by dark and light and melatonin without influence of time of day. | melanophores were studied in tadpoles of the south african clawed toad, xenopus laevis, during the first week after hatching (stages 46-49) at 25 degrees c. the tadpoles had melanophores with dispersed melanosomes in the light and punctate melanophores in the dark in ld 12:12. the melanophores remained punctate in constant dark and the melanosomes remained dispersed in constant light. lights-out (in the light-time of ld 12:12) caused the melanophores to become punctate, which occurred more quick ... | 1988 | 3367263 |
| differential stimulation of sea urchin early and late h2b histone gene expression by a gastrula nuclear extract after injection into xenopus laevis oocytes. | sea urchin early histone genes are active in preblastula embryos; late histone genes are maximally expressed during subsequent stages of embryogenesis. we used the xenopus laevis oocyte to assay for trans-acting factors involved in this differential regulation. sea urchin nuclear proteins were prepared by extracting gastrula-stage chromatin successively with 0.45, 1, and 2 m nacl. we injected three fractions into oocytes along with plasmids bearing sea urchin early and late h2b histone genes. wh ... | 1988 | 3367908 |
| purification, immunological and biochemical characterization of ap4a binding protein from xenopus laevis oocytes. | diadenosine 5',5'''-p1,p4-tetraphosphate (ap4a) binding protein specifically binds ap4a. the protein has been purified from xenopus laevis oocytes and presents an estimated molecular weight of 100,000 by gel filtration. in the first stages of the purification, the ap4a binding activity is found associated to dna polymerase alpha-dna primase, forming heterogeneous high molecular weight complexes. a monoclonal antibody has been prepared against the purified ap4a binding protein. the antibody parti ... | 1988 | 3368311 |
| factors involved in the formation and stabilization of cell aggregates obtained from amphibian embryonic explants. | the effect of factors influencing the formation and stability of animal and vegetal aggregates from xenopus laevis and ambystoma mexicanum was examined in the light and scanning electron microscopes. at extreme values of ph the surface coat covering the vegetal aggregates is dissolved and dissociation may take place. animal aggregates are more resistant. at high tonicities vegetal aggregates may be dissociated, and in the animal aggregates the epidermal differentiation is suppressed. in the abse ... | 1988 | 3370680 |
| the primary structure of rat ribosomal protein l18. | the amino acid sequence of rat ribosomal protein l18 was deduced from the sequence of nucleotides in a recombinant cdna and confirmed from the amino-terminal amino acid sequence of the protein. ribosomal protein l18 contains 187 amino acids (the amino-terminal methionine is removed after translation of the mrna) and has a molecular weight of 21,530. hybridization of the cdna to digests of nuclear dna suggests that there are 10-14 copies of the l18 gene. rat ribosomal protein l18 is homologous to ... | 1988 | 3371159 |
| how is the flagellar length of mature sperm determined? i. comparison of flagellar growth in spermatids between newt and xenopus in vitro. | the kinetics of flagellar growth in round spermatids were compared between xenopus laevis and cynops pyrrhogaster in vitro, the latter of which has about 13 times longer flagella in mature sperm than the former. in both species, more than 90% of the spermatids derived from marked primary spermatocytes grew flagella. in xenopus the average flagellar length increased to 28 microns by the 6th day and then stopped growth, while in the newt, flagellar growth did not stop until reaching 107 microns in ... | 1988 | 3371423 |
| a new repetitive protein from xenopus laevis skin highly homologous to pancreatic spasmolytic polypeptide. | a cdna sequence has been used to derive the precursor structure of a highly repetitive protein in xenopus laevis skin. from the sequence of a whole family of secretory proteins can be predicted containing a classical hydrophobic signal sequence at the nh2-terminal end of the precursor. the proteins contain four domains with high homology to porcine pancreatic spasmolytic polypeptide. these four cysteine-rich, presumably physiologically active domains are separated in the molecule by a repetitive ... | 1988 | 3372504 |
| human low density lipoprotein receptor expressed in xenopus oocytes. conserved signals for o-linked glycosylation and receptor-mediated endocytosis. | the human low density lipoprotein (ldl) receptor is shown to carry out efficient receptor-mediated endocytosis in xenopus laevis oocytes. microinjection of mrnas encoding the human receptor led to synthesis of a 120-kda precursor possessing high mannose n-linked sugars and core o-linked sugars. during its transport to the cell surface, the protein increased in apparent size to 160 kda, which is similar to the change that occurs in human cells. this increase was not seen when the receptor lacked ... | 1988 | 3372507 |
| selective binding of colloidal gold-protein conjugates to secretory granules of granular skin glands and myelin sheaths in the skin of xenopus laevis. | colloidal gold-protein conjugates are widely used in immunoelectron microscopical studies as general "second antibody" markers. this report demonstrates that colloidal gold conjugated with goat anti-mouse immunoglobulin g (igg), protein a, and bovine serum albumin (bsa) binds selectively to secretory granules of granular skin glands and myelin sheaths in the skin of xenopus laevis. the gold labeling pattern was identical whether goat anti-mouse igg, protein a, or bsa was used to stabilize the co ... | 1988 | 3373068 |
| different regulatory elements are required for cell-type and stage specific expression of the xenopus laevis skeletal muscle actin gene upon injection in x.laevis oocytes and embryos. | in the present study, we demonstrate by transcript mapping that the injected xenopus skeletal muscle alpha-actin gene is transcribed and spliced in xenopus oocytes but not correctly initiated at the alpha-actin promoter. this leads to correctly spliced transcripts even if constructs without putative promoter sequences are injected. on the other hand, alpha-actin transcripts are translated in injected oocytes as shown by the detection of alpha-actin protein. by contrast, correctly initiated alpha ... | 1988 | 3375055 |
| the organisation and expression of histone genes from xenopus borealis. | we have isolated genomic clones from xenopus borealis representing 3 different types of histone gene cluster. we show that the major type (h1, h2b, h2a, h4, h3), present at about 60-70 copies per haploid genome (1), is tandemly reiterated with a repeat length of 15 kb. in situ hybridization to mitotic chromosomes shows that the majority of histone genes in xenopus borealis are at one locus. this locus is on the long arm of one of the small sub-metacentric chromosomes. a minor cluster type with t ... | 1988 | 3375060 |
| electron microscopic study of crystals of the xenopus laevis transcription factor iiia-5s ribosomal rna complex. | a novel method has been developed to grow crystals of the xenopus laevis transcription factor iiia-5s rna complex directly on grids for examination by electron microscopy. microcrystals were examined in negative stain and in thin sections to reveal a hexagonal lattice with unit-cell dimensions a = b = 87.1 +/- 4.4 a and c = 143.8 +/- 12.7 a. optical diffraction patterns from micrographs were obtained about the major crystal axes extending to about 40-a resolution. a packing scheme is proposed fo ... | 1988 | 3375242 |
| the development of acetylcholinesterase activity in the embryonic nervous system of the frog, xenopus laevis. | histochemical detection of acetylcholinesterase (ache) activity in xenopus embryos was found first in primary motoneurons, rohon-beard neurons and somitic myotubes at early tail bud stages. at late tail bud stages all primary neurons, including primary interneurons, cranial ganglion cells and ventral brainstem cells expressed this enzyme. the onset of detectable ache activity in some primary neurons occurred near the time of initial axon outgrowth, whereas in others it occurred at much later sta ... | 1988 | 3378171 |
| analysis of proteins in the peripheral and central regions of amphibian oocytes and eggs. | proteins in oocytes, meiotically mature eggs and zygotes of xenopus laevis were examined to determine whether proteins in the peripheral region differ from those in the central region of these cells. we show that different regions contain different amounts of newly synthesized proteins and that during meiotic maturation and fertilization the periphery of the animal hemisphere becomes the site where most newly synthesized proteins are found. examination of two-dimensional gels indicates that most ... | 1988 | 3378266 |
| cell to cell adhesion systems in xenopus laevis, the south african clawed toad. ii: monoclonal antibody against a novel ca2+-dependent cell-cell adhesion glycoprotein on amphibian cells. | we isolated a mouse monoclonal antibody that disrupts ca2+-dependent cell-cell adhesion of amphibian (xenopus laevis) cells. when added to culture medium, the monoclonal antibody completely disrupted cell-cell adhesion of amphibian cells in monolayer culture and specifically inhibited ca2+-dependent cell-cell adhesion of dissociated cells in reaggregation experiments. the monoclonal antibody recognized a 140 kda cell surface glycoprotein antigenically different from the previously reported ca2+- ... | 1988 | 3378270 |
| responses in xenopus to the thymus independent antigen polyvinylpyrrolidone (pvp) and its haptenated derivative, trinitrophenylated pvp (tnp-pvp). | xenopus laevis (the south african clawed toad) can respond to thymus dependent (td) and thymus independent (ti) antigens. however, the response to trinitrophenylated ficoll (tnp-ficoll), a ti-2 antigen in mammals, is thymus dependent in xenopus. polyvinylpyrrolidone (pvp), classed as a ti antigen in mammals, is also a ti antigen in xenopus, but responses to pvp and tnp-pvp are thymus regulated. as with tnp-ficoll, capacity to respond to tnp-pvp diminishes during metamorphosis, and tolerance can ... | 1988 | 3378271 |
| persistence and replication of plasmid dna microinjected into early embryos of xenopus laevis. | the persistence and replication of defined circular and linear plasmid dna molecules microinjected into fertilized eggs of xenopus laevis were analyzed. for all plasmids tested, a small fraction of microinjected circular molecules was replicated; however, the overall copy numbers of either free form i or form ii molecules usually did not increase through blastulation. in contrast, extensive amplification of input dna sequences was seen whenever the microinjected dna was assembled into high molec ... | 1988 | 3378672 |
| circadian regulation of retinomotor movements: ii. the role of gaba in the regulation of cone position. | cone photoreceptor movements in lower vertebrates are regulated by the interaction of the light-dark cycle and an endogenous circadian clock. we have suggested that melatonin and dopamine interact to regulate dark- and light-adaptive movements, respectively, and that melatonin affects cones indirectly by inhibiting dopamine release. in fact, any factor modulating dopaminergic neurons in the retina may have effects on either cone elongation or contraction. we have utilized an in vitro eyecup prep ... | 1988 | 3379159 |
| replacement of maternal 40s rrna precursor by newly synthesized precursor in early embryos of xenopus laevis. | the amount of intact 40s rrna precursor was followed by northern hybridization in the course of the early embryogenesis of wild-type xenopus laevis and its anucleolate mutant. the total amount of 40s rrna precursor did not alter appreciably until the midblastula stage, decreased at the late blastula stage, and then increased. in the anucleolate mutant, in which no rrna synthesis occurs, the 40s rrna precursor decreased at the late blastula stage and disappeared after the gastrula stage. in the n ... | 1988 | 3383250 |
| relationship of promagainin to three other prohormones from the skin of xenopus laevis: a different perspective. | we observed a striking sequence similarity between precursors for promagainin and procaerulein type i (excluding the caerulein peptide region). additional comparisons of the promagainin precursor with those of other procaeruleins, proxenopsin, and peptide-gly-leu-amide revealed that all possess one or more copies of a structurally similar spacer module, from which an amphiphilic spacer peptide is cleaved. promagainin yields the magainins, spacer peptides with antimicrobial activity; we suggest o ... | 1988 | 3384094 |
| the first cleavage plane and the embryonic axis are determined by separate mechanisms in xenopus laevis. ii. experimental dissociation by lateral compression of the egg. | in eggs of xenopus laevis, the meridian of sperm entry (sep meridian), the direction of subcortical rotation, and the first cleavage furrow have been used to predict, with varying degrees of accuracy, the position of the plane of bilateral symmetry of the embryo. we show here that altering the shape of the uncleaved egg by lateral compression disrupts some of these topographical relationships in a reproducible way. the neural groove, which identifies the embryonic dorsal midline, usually forms a ... | 1988 | 3384178 |
| quantitative relationships between motoneuron and muscle development in xenopus laevis: implications for motoneuron cell death and motor unit formation. | a common approach to the study of neural regression has been to correlate the timing of cell loss with other events such as target development. most of these studies have areas of uncertainty. first, the analysis is normally carried out on groups of neurons that innervate a variety of targets. second, there are some doubts about the reliability of light microscopic quantitation of muscle development. in this study, the period of cell death in the semimembranosus motor pool of xenopus laevis has ... | 1988 | 3385009 |
| identification of xenopus laevis sperm and egg envelope binding components on nitrocellulose membranes. | interacting egg envelope and sperm surface components were identified for xenopus laevis using blotting methods. sperm were extracted with sodium dodecyl sulfate (sds), the extracted proteins separated by gel electrophoresis and blotted, and the blots treated with 125i-labeled heat solubilized envelopes. the converse experiment was also performed where envelope components were separated by gel electrophoresis, blotted, and the blots treated with 125i-labeled sperm components. blotted sperm compo ... | 1988 | 3385369 |
| enolase isoenzymes in adult and developing xenopus laevis and characterization of a cloned enolase sequence. | as part of a study of glycolysis during early development we have examined the pattern of expression of enolase isoenzymes in xenopus laevis. in addition, the nucleotide sequence of a cdna clone coding for the complete amino acid sequence of one enolase gene (eno1) in x. laevis was determined. x. laevis eno1 shows highest homology to mammalian non-neuronal enolase. analysis of enolase isoenzymes in x. laevis by non-denaturing electrophoresis on cellulose acetate strips revealed five isoenzymes. ... | 1988 | 3390159 |
| characterization of a proteolytic enzyme in the skin secretions of xenopus laevis. | enzymes present in the skin secretions of xenopus laevis were fractionated by ion exchange chromatography. one of the proteases obtained was found to catalyse cleavage on the cooh-side of peptide sequences containing consecutive hydrophobic and basic residues. evidence is presented that the enzyme is a cysteine protease with an optimum ph of 5.0 to 6.0. the characteristic specificity of this enzyme suggests that it may fulfil a role in propeptide processing. | 1988 | 3390179 |
| effects of the xenopus laevis mitochondrial single-stranded dna-binding protein on the activity of dna polymerase gamma. | the single-stranded dna-binding protein from xenopus laevis oocyte mitochondria, which has been found associated with the d loop, binds to ssdna in stoichiometric amounts and can under certain conditions stimulate the activity of the dna polymerase gamma. its properties suggest that it is involved in strand displacement during the replication of the mitochondrial genome. | 1988 | 3391165 |
| electron microscopic visualization of sites of nascent dna synthesis by streptavidin-gold binding to biotinylated nucleotides incorporated in vivo. | biotinylated nucleotides (bio-11-dctp, bio-11-dutp, and bio-7-datp) were microinjected into unfertilized and fertilized xenopus laevis eggs. the amounts introduced were comparable to in vivo deoxy-nucleoside triphosphate pools. at various times after microinjection, dna was extracted from eggs or embryos and subjected to electrophoresis on agarose gels. newly synthesized biotinylated dna was analyzed by southern transfer and visualized using either the blugene or detek-hrp streptavidin-based nuc ... | 1988 | 3392102 |
| protein kinase activity associated with stored messenger ribonucleoprotein particles of xenopus oocytes. | as the oocytes of xenopus laevis grow and develop they accumulate vast stores of mrna for use during early embryogenesis. the stored mrna is stabilized and may be prevented from being translated in oocytes by the binding of a defined set of oocyte-specific proteins to form messenger rnp (mrnp) particles. a key event in the interaction of protein with mrna is the phosphorylation of those few polypeptides that bind directly to all classes of polyadenylated mrna. in this study we show that the phos ... | 1988 | 3392105 |
| a trypsin-sensitive receptor on membrane vesicles is required for nuclear envelope formation in vitro. | the reformation of functioning organelles at the end of mitosis presents a problem in vesicle targeting. using extracts made from xenopus laevis frog eggs, we have studied in vitro the vesicles that reform the nuclear envelope. in the in vitro assay, nuclear envelope growth is linear with time. furthermore, the final surface area of the nuclear envelopes formed is directly dependent upon the amount of membrane vesicles added to the assay. egg membrane vesicles could be fractionated into two popu ... | 1988 | 3392106 |
| sex differences in the motor nucleus of cranial nerve ix-x in xenopus laevis: a quantitative golgi study. | in the clawed frog (xenopus laevis), motor neurons in cranial nerve nucleus ix-x control contraction of laryngeal muscles responsible for sexually dimorphic vocal behaviors. we examined sex differences in dendritic arbors of n.ix-x cells using the golgi-cox method. three morphological classes of somal types (ovoid, triangular, and elongate) are present in similar frequencies in n.ix-x of both males and females. the male n.ix-x neuron is a more complex and hypertrophied version of the female n.ix ... | 1988 | 3392529 |
| [mrna for the plasminogen activator of the urokinase type: translation in oocytes of xenopus laevis]. | poly(a)+-rna from human kidney and human embryonal lung fibroblasts fractionated by sucrose gradient centrifugation was translated in xenopus oocytes. assay for plasminogen-dependent fibrinolytic activity detected synthesis of secreted plasminogen activator and revealed the active fraction of poly(a)+-rna with a sedimentation coefficient of approximately 23s. translation products of the active fraction were immunoadsorbed by antiurokinase monoclonal antibodies immobilized on sepharose. gel elect ... | 1988 | 3393155 |
| monoclonal antibodies against larval nervous system of xenopus laevis: their specificities and application to analysis of neural development. | monoclonal antibodies were raised against larval tissues from xenopus laevis. two of them which bound to neural tissue were examined for their cytological specificities by indirect immunofluorescence on larval frozen sections. one of the monoclonal antibodies (nm1) had affinity for both neural and muscular tissues, while the other (n1) bound exclusively to neural tissue. nm1 was shown in the neural tissue to possess a high affinity for the axons from a large population of neurons and possibly th ... | 1988 | 3393282 |
| morphological classification of retinal ganglion cells in adult xenopus laevis. | retrograde transport of horseradish peroxidase (hrp) was used to characterise the soma and dendritic arborization of retinal ganglion cells in adult xenopus laevis toad. hrp was administered to the cut end of the optic nerve and the morphological characteristics of hrp-filled ganglion cells were analysed in retinal wholemount preparations using computer assisted morphometry. ganglion cells were classified according to their soma size, dendritic branching pattern, dendritic field and the number o ... | 1988 | 3394956 |
| reversal of dorsoventral polarity in xenopus laevis embryos by 180 degrees rotation of the animal micromeres at the eight-cell stage. | the 180 degrees rotation of the animal cell quartet at the 8-cell stage of xenopus laevis embryos leads to a reversal of dorsoventral polarity in a majority of the embryos. dorsal micromeres appear to instruct the macromeres in contact with them to initiate later steps in dorsal development. this inductive process is most apparent in the second half of the third cell cycle and is largely lost by the beginning of the fourth cell cycle. | 1988 | 3396766 |
| homologous genes for mouse 4.5s hybrna are found in all eukaryotes and their low molecular weight rna transcripts intermolecularly hybridize with eukaryotic 18s ribosomal rnas. | previous work has reported the isolation and sequencing of a mouse low molecular weight rna species designated 4.5s hybridizing rna or hybrna because of its ability to intermolecularly hybridize with mouse mrna and 18s rrna sequences. using synthetic dna oligonucleotide probes we have examined the conservation of this gene sequence and its expression as a lmwrna transcript across evolution. southern blot analysis has shown that homologous genes of single or low copy number are found in all eukar ... | 1988 | 3399384 |
| transcription complexes that program xenopus 5s rna genes are stable in vivo. | the long-term stability of transcription complexes on 5s rna genes has been demonstrated in vivo. complexes on oocyte and somatic-type 5s rna genes injected into xenopus laevis oocyte nuclei are stable for at least 4 days. tissue culture cells and mature erythrocytes have equivalent numbers of somatic 5s rna genes programmed into transcription complexes, yet the former cell type has a greater than 50-fold higher cellular content of transcription factor iiia (tfiiia). functional transcription com ... | 1988 | 3399503 |
| comparison of a carboxypeptidase e-like enzyme in human, bovine, mouse, xenopus, shark and aplysia neural tissue. | several diverse species contain an enzyme with many properties in common with those of bovine carboxypeptidase e (cpe), a neuropeptide processing carboxypeptidase b-like enzyme. this enzyme has been designated ec 3.4.17.10, and is also known as enkephalin convertase and carboxypeptidase h. all tissues that are known to contain bioactive peptides also contain cpe-like enzymatic activity. in xenopus laevis, enzyme activity is highest in the brain and pituitary, lower in the skin, and undetectable ... | 1988 | 3401766 |
| calcium sensitivity of microtubules changes during the cell cycle of xenopus laevis tadpole endothelial cells. | endothelial cells derived from xenopus tadpole hearts (xth-2: schlage et al. 1981) have been permeabilized for calcium using the ionophore a 23187. a ca2+-concentration of 1 microm causes a graded disassembly of microtubules (mts): with increasing periods of incubation mts disintegrate and then depolymerize completely. the frequency of the different stages of depolymerization depends on the length of the ca2+ incubation period, even after 60 min incubation time some mts remain. the stage of depo ... | 1988 | 3401933 |
| template sequences required for transcription of xenopus laevis mitochondrial dna from two bidirectional promoters. | previous work from our laboratory has shown that transcription of xenopus laevis mitochondrial dna initiates both in vivo and in vitro from bidirectional promoters located between the gene for trna(phe) and the 5' termini of displacement loop dna strands. a consensus sequence matching the octanucleotide acgttata surrounds each transcription start site. in the present study, we used in vitro mutagenesis to define sequences required for specific transcription in vitro. first, cloned mitochondrial ... | 1988 | 3405223 |
| protein kinase c mediates neural induction in xenopus laevis. | inductive cell interactions are essential in early embryonic development, but virtually nothing is known about the molecular mechanisms involved. recently factors resembling fibroblast growth factor and transforming growth factor-beta were shown to be involved in mesoderm induction in xenopus laevis, suggesting that membrane receptor-mediated signal transduction is important in induction processes. here we report direct measurements of protein kinase c (pkc) activity in uninduced ectoderm, and i ... | 1988 | 3405309 |
| in vitro proliferation and differentiation of myogenic cells from adult xenopus. | a technique is described for isolating amphibian myogenic cells from the muscle of adult xenopus laevis (dauchin). muscles were dissociated with 0.2% collagenase and 0.1% trypsin. the resulting cell suspensions were separated from the remaining myofibres by filtration through nylon grids. most of the cells remaining in the filtrate suspension were satellite cells or fibroblasts. when plated in petri dishes, satellite cells adhered to the substrate, became spindle-shaped and proliferated activity ... | 1988 | 3408748 |
| close juxtaposition between inducing chordamesoderm and reacting neuroectoderm is a prerequisite for neural induction in xenopus laevis. | the results of this study indicate that the induction of the central nervous system in xenopus laevis depends on the close juxtaposition of inducing chordamesoderm and reacting ectoderm, which is necessary for the short distance migration of neural inducing factors. the examination of the neuroectoderm-chordamesoderm interface at intervals of 1 h up to 5 h showed that the onset of neural induction is correlated to the degree of contact formation between ectodermal and mesodermal cells. in the ec ... | 1988 | 3409323 |
| accumulation and decay of dg42 gene products follow a gradient pattern during xenopus embryogenesis. | the dg42 gene is expressed during a short window during embryogenesis of xenopus laevis. the mrna for this gene can be first detected just after midblastula, peaks at late gastrula, and decays by the end of neurulation. the sequence of the dg42 cdna and genomic dna predicts a 70,000-da protein that is not related to any other known protein. antibodies prepared against portions of the dg42 open reading frame that had been expressed in bacteria detected a 70,000-da protein in the embryo with a tem ... | 1988 | 3410156 |
| a ventrally localized inhibitor of melanization in xenopus laevis skin. | melanophores normally differentiate in dorsal but not in ventral skin of xenopus laevis. we have sought factors which might regulate this differentiation pattern, and we have obtained a putative melanization inhibiting factor (mif) from ventral but not from dorsal skin. preliminary studies reveal that mif is destroyed by heat or trypsin treatment, indicating its protein composition, and has a molecular weight in the range of 300 kda. the effects of mif on the differentiation of neural crest deri ... | 1988 | 3410161 |
| corticosteroid receptors in liver cytosol of the clawed toad, xenopus laevis: daily and seasonal variations. | in postmetamorphic xenopus laevis liver cytosol the glucocorticoid binding capacity r0 and the dissociation constant kd were determined. the receptor assay included an incubation period of 24 hr at 0-4 degrees with sodium molybdate to stabilize the receptor. dexamethasone, triamcinolone acetonide, and corticosterone as tritiated ligands were compared regarding the r0 (67.6, 57.2, and 30.7 fmol/mg protein), the kd (3.54, 0.56, and 9.03 nm), and the rate of dissociation in young specimens of x. la ... | 1988 | 3410292 |
| monoclonal autoantibodies recognizing histone variants. | balb/c mice were immunized with affinity purified ro(ss-a) from human origin in order to allow the preparation of monoclonal anti-ro(ss-a) antibodies. after fusion of mouse myeloma cells (line sp2/0 a914) with spleen cells from one of these mice, anti-ro(ss-a) monoclonals were not obtained, but, instead, two igm producing hybridomas reactive with histone h1 and one with histone h2b. the specificity of the anti-h1 monoclonals was investigated by means of immunoblotting of very lysine-rich histone ... | 1988 | 3410513 |
| digit regeneration in the hindlimbs of larval stages of xenopus laevis (daudin). | | 1988 | 3412344 |
| a membrane-associated dimer of acetylcholinesterase from xenopus skeletal muscle is solubilized by phosphatidylinositol-specific phospholipase c. | the susceptibility to phosphatidylinositol-specific phospholipase c of the membrane associated acetylcholinesterase (ache) forms of xenopus laevis skeletal muscle was examined. this treatment released almost all the detergent-soluble ache species from muscle homogenates. sucrose gradient analysis showed that the released acetylcholinesterase form corresponds to a hydrophilic g2 dimer, indicating that this dimer has a glycolipid anchoring domain which contains phosphatidylinositol. | 1988 | 3412641 |
| cdna and deduced primary structure of rat protein b23, a nucleolar protein containing highly conserved sequences. | protein b23 (mr/pi = 38,000/5.1) is a major rna-associated nucleolar phosphoprotein which contains highly acidic segments and has a high affinity for silver ions. using synthetic oligonucleotides as probes cloned cdnas encoding protein b23 were isolated and characterized. one of the cdnas, obtained from a rat brain library, contained an insert of 1232 base pairs of dna encoding a polypeptide of 292 amino acid residues. segments of the protein sequence were confirmed by partial sequencing of cnbr ... | 1988 | 3417636 |
| purification of transcription factor iiib from hela cells. | transcription factor iiib (tfiiib), which by itself does not bind stably or specifically to dna, was purified from cytoplasmic extracts of hela cells using five different chromatographic steps. this procedure yields one predominant polypeptide which represents 90% of the most highly purified preparation and shows a relative molecular mass of 60,000, when analyzed on sodium dodecyl sulfate-polyacrylamide gels. a similar value was obtained for the native protein by rate zonal centrifugation on gly ... | 1988 | 3417660 |
| the extracellular matrix of xenopus laevis eggs: a quick-freeze, deep-etch analysis of its modification at fertilization. | eggs of the amphibian, xenopus laevis, were quick-frozen, deep-etched, and rotary-shadowed. the structure of the extracellular matrix surrounding these eggs, including the perivitelline space and the vitelline envelope (ve), was visualized in platinum replicas by electron microscopy. the perivitelline space contains an elaborate filamentous glycocalyx which connects microvillar tips to the plasma membrane, to adjacent microvilli, and to the overlying ve. the ve is comprised of two layers, the in ... | 1988 | 3417770 |
| locations of methyl groups in 28 s rrna of xenopus laevis and man. clustering in the conserved core of molecule. | 28 s ribosomal rna from several vertebrate species contains some 68 to 70 methyl groups. evidence described in this paper enables some 58 methyl groups to be located in the primary structure of 28 s ribosomal rna from xenopus laevis. most of the locations are unambiguous but a few are currently tentative. in human 28 s ribosomal rna the great majority of the same sites are methylated as in xenopus, but there are a few differences between the respective methyl group distributions. the main featur ... | 1988 | 3418702 |
| synergism of closely adjacent estrogen-responsive elements increases their regulatory potential. | recent gene transfer experiments have shown that an estrogen-responsive dna element (ere) ggtcannntgacc mediates the estrogen inducibility of the xenopus laevis vitellogenin a1 and a2 genes as well as the chicken vitellogenin ii gene. we report here on experiments that explain the estrogen regulation of the xenopus vitellogenin b1 and b2 genes. in these genes, two ere homologues, which have only low, if any, regulatory capacity on their own, act synergistically to achieve high estrogen inducibil ... | 1988 | 3418708 |
| an elongated model of the xenopus laevis transcription factor iiia-5s ribosomal rna complex derived from neutron scattering and hydrodynamic measurements. | the precise molecular composition of the xenopus laevis tfiiia-5s ribosomal rna complex (7s particle) has been established from small angle neutron and dynamic light scattering. the molecular weight of the particle was found to be 95,700 +/- 10,000 and 86,700 +/- 9000 daltons from these two methods respectively. the observed match point of 54.4% d2o obtained from contrast variation experiments indicates a 1:1 molar ratio. it is concluded that only a single molecule of tfiiia, a zinc-finger prote ... | 1988 | 3419928 |
| effect of denervation of carotid labyrinths on breathing in unrestrained xenopus laevis. | the effect of denervation of the carotid labyrinths on breathing responses to simultaneously applied aerial and aquatic normoxia, hypoxia, or hypercapnia has been studied in unrestrained xenopus laevis. denervation significantly reduced vi of normoxic toads compared with vi in intact and sham-operated toads, due to a significant reduction in the volume of each buccal pumping movement (vb) in denervates. breathing increased significantly in response to environmental hypoxia or hypercapnia in inta ... | 1988 | 3420325 |
| purification and characterization of a casein-kinase-ii-type enzyme from xenopus laevis ovary. biological effects on the meiotic cell division of full-grown oocyte. | a casein kinase of type ii has been highly purified from xenopus laevis ovary. a new experimental protocol has been developed for the purification, consisting in four chromatographic steps: hydrophobic on tyrosine-agarose, ion exchange on deae-sepharose, affinity on heparin-sepharose and fast protein liquid on mono q. the purification was greater than 20,000, taking into account an inhibitor present in the starting material which masked the activity in the crude fraction. the overall yield was g ... | 1988 | 3422187 |
| selective visualization of gene structure with ultraviolet light. | the ability of the ultraviolet (uv) "footprinting" technique to detect chromatin has been investigated in vitro. two basic types of chromatin, a phased nucleosome and a phased nucleosome containing a phased h1 protein, have been reconstituted onto a cloned 5s ribosomal rna gene from sea urchin. the histone-dna interactions in each complex have been probed with exonuclease iii, dnase i, dimethyl sulfate, and uv light. whereas dnase i and exonuclease iii readily detect interactions between histone ... | 1988 | 3422448 |
| properties of a high-affinity dna binding site for estrogen receptor. | it has been shown previously that a short sequence from the 5' regulatory region of the xenopus laevis vitellogenin gene a2, when appropriately placed, can confer estrogen responsiveness to another gene. using the xenopus sequence and similar sequences from the 5' regulatory regions of other estrogen-responsive genes, we derived a consensus sequence 38 nucleotides long. the sequence contains an inverted repeat (5' c-a-g-g-t-c-a-g-a-g-t-g-a-c-c-t-g 3') and an a/t-rich region. plasmids carrying a ... | 1988 | 3422476 |
| xenopus laevis hemoglobin and its hybrids with hemoglobin a+. | isolated alpha and beta chains from xenopus laevis hemoglobin have been purified. the isolation procedure yields native alpha chains whose functional behavior has been characterized and compared with that of human alpha chains. isolated beta chains in the presence of oxygen are characterized by low stability, and hence their functional characterization was limited to the co binding kinetics. when stoichiometric amounts of the isolated alpha and beta chains are mixed, a tetramer characterized by ... | 1987 | 3427040 |
| visualization of secretory activities in the xenopus neurohypophysis by a high s/n video camera. | the optical turbidity of neurohypophyses of the frog xenopus laevis was observed with the help of a high signal to noise ratio video camera and a high speed image processor. electrical stimulation of the pituitary stalk induced a decrease in turbidity of the neurohypophysis. this response was visualized on a monitor screen as a diffuse pattern consisting of many bright spots. the diameters of these spots were similar to those of individual nerve terminals, indicating that the optical response ar ... | 1987 | 3427467 |
| pyruvate kinase isozymes in oocytes and embryos from the frog xenopus laevis. | 1. the kinetic characteristics of pyruvate kinase isozymes from oocytes, embryos, liver and skeletal muscle from the clawed frog xenopus laevis were measured in cell extracts. 2. the muscle and liver isozymes display michaelis-menten kinetics with kms for phosphoenolpyruvate (pep) of 0.02 and 0.05 mm, respectively. 3. pyruvate kinase from oocytes and embryos displays cooperative kinetics for pep with a km of about 0.15 mm; the kinetics become hyperbolic and the km for pep is reduced to 0.05 mm i ... | 1987 | 3427912 |
| nuclear lamin li of xenopus laevis: cdna cloning, amino acid sequence and binding specificity of a member of the lamin b subfamily. | lamins are karyoskeletal proteins associated with the nuclear envelope which can be divided into two groups, i.e. the type a lamins of near neutral pi and the more acidic lamins, including mammalian lamin b. we have isolated cdna clones encoding a representative of the type b subfamily from xenopus laevis, and have deduced its amino acid sequence from the coding portion of the approximately 2.9 kb mrna. the polypeptide (mol. wt 66,433) is identified as a typical lamin by its homology to xenopus ... | 1987 | 3428276 |
| endocytosis in the inner segment of rod photoreceptors: analysis of xenopus laevis retinas using horseradish peroxidase. | to evaluate endocytosis in rod photoreceptor inner segments, isolated retinas from xenopus laevis were maintained in vitro in the presence of the tracer, horseradish peroxidase (hrp). hrp-positive vesicles, 110 +/- 82 nm in diam. (mean +/- s.d.), appeared in the inner segment cytoplasm within 2 min of incubation. within 8-15 min, 20-30% of the vesicles in the ellipsoid were hrp-positive, reaching approx. 50% by 30-60 min and maintaining this level through 4 hr of culture. in retinas incubated 30 ... | 1987 | 3428395 |
| differential accumulation of u1 and u4 small nuclear rnas during xenopus development. | we showed previously that those u1 small nuclear rna (snrna) genes of xenopus laevis which are transcribed very actively in early embryos are quiescent in mature (stage vi) oocytes (forbes et al. 1984). although that study demonstrated that differential control of snrna genes occurred, it did not describe snrna accumulation during development. using high-resolution polyacrylamide gels in combination with northern blot hybridization and rna sequence analyses, we show here that xenopus has at leas ... | 1987 | 3428589 |
| the transcription of xenopus laevis embryonic u1 snrna genes changes when oocytes mature into eggs. | x. laevis stage vi oocytes respond differently from unfertilized eggs when injected with the genes for x. laevis embryonic u1 rnas, xu1b1, and xu1b2. upon maturation of oocytes into eggs, the efficiency of transcription decreases greatly and the ratio of xu1b1 to xu1b2 rna transcription changes. moreover, dna replication is now required for transcription. because of differences in the 5'-flanking regions of the two xu1b genes, xu1b2 rna transcription predominates after injection into oocytes; in ... | 1987 | 3428590 |
| cloning of nucleoplasmin from xenopus laevis oocytes and analysis of its developmental expression. | nucleoplasmin is the most abundant protein in the nucleus of xenopus laevis oocytes. we cloned a cdna coding for nucleoplasmin from an expression library of immature xenopus laevis oocytes. the deduced amino acid sequence shows that the carboxyl terminus is very hydrophilic and contains an unusual stretch of 12 glutamic acid residues, which is consistent with one of the proposed functions of nucleoplasmin--that of promoting chromatin assembly. the last 50 amino acids are lysine- and alanine-rich ... | 1987 | 3428591 |
| the trochlear nerve of amphibians and its relation to proprioceptive fibers: a qualitative and quantitative hrp study. | the cells of origin of the trochlear nerve of urodeles, anurans and gymnophionans were labelled with hrp in order to compare the location and morphology of trochlear motoneurons and to find evidence for sensory fibers in the trochlear nerve of amphibians. trochlear motoneuron perikarya were found in a ventral tegmental position predominantly on the contralateral side, but an ipsilateral cell was present in some specimens of urodeles and anurans. about 19 motoneurons were labelled in ambystoma, a ... | 1987 | 3434841 |
| properties of a distal regulatory element controlling transcription of the u2 small nuclear rna. | the upstream region of human u2 genes contains a distal transcriptional control element, previously mapped between nucleotide (nt) positions -198 and -258 (westin et al., 1984b). in the present study we show that it resembles transcriptional enhancers in being active even from a distance of 1.4 kb. however, in contrast to most other enhancers it functions unidirectionally in xenopus laevis oocytes. the distal control element was further mapped by construction of truncated templates for u2 rna tr ... | 1987 | 3436529 |
| the activation of amplified ribosomal rna genes in the oocytes of xenopus laevis: an electron microscope analysis. | | 1987 | 3436833 |
| the distribution of motoneurons supplying hind limb muscles in the clawed toad, xenopus laevis. | the distribution of motoneurons in the lumbar spinal cord (spinal segments 8-10) of the clawed toad, xenopus laevis, was studied with the horseradish peroxidase technique. in a total of 13 different hind limb muscles this tracer was applied in a slow-release gel. motoneurons innervating a particular hind limb muscle were clustered in longitudinally arranged motor pools. motor pools of different muscles did show considerable overlap both in the rostrocaudal and transverse plane. but, the various ... | 1987 | 3439496 |
| atlas of adult xenopus laevis laevis hematology. | | 1987 | 3440505 |
| purification of a novel, nucleoplasmin-like protein from somatic nuclei. | we have purified a nucleoplasmin-like protein from the nuclei of somatic xenopus laevis cells. this protein possesses a number of the distinctive features of nucleoplasmin isolated from oocytes or unfertilized eggs. the protein is recognized by both monoclonal and polyclonal antisera raised against egg nucleoplasmin. the protein has an oligomeric structure, which must be heated in sds to completely dissociate, is acidic, phosphorylated and efficiently promotes the in vitro formation of chromatin ... | 1987 | 3443097 |
| stable maintenance heat rate and contractile properties of different single muscle fibres from xenopus laevis at 20 degrees c. | 1. different types of fibres were isolated from the iliofibularis muscle of xenopus laevis. resting length was adjusted to obtain a sarcomere length of 2.3 microns as judged by laser diffraction. heat production was measured during tetanic contractions lasting 0.3-2 s at 20 degrees c. from twenty fibres the force-velocity relationship was determined as well. 2. after correcting the records for heat loss, and taking the relevant heat capacities into account, stable maintenance heat rate was deter ... | 1987 | 3446801 |
| mapping at the nucleotide level of xenopus laevis mitochondrial d-loop h strand: structural features of the 3' region. | the d-loop resulting from limited synthesis of the newly replicated heavy (h) strand of mitochondrial dna provides a good opportunity to examine both the origin and termination of dna synthesis. we report here the precise determination of the 3' and 5' termini of nascent xenopus laevis d-loop h strand. we observe two major classes of newly synthesized d-loop h strands, 1641 and 1675 nucleotides long. a stable putative secondary structure located around its 3' end is described. analogous secondar ... | 1987 | 3453088 |
| characterization of three sites of rna 3' end formation in the xenopus ribosomal gene spacer. | we have studied three sites of 3' end formation on the xenopus laevis ribosomal genes, designated t1, t2, and t3. site t1 coincides with the unique hindiii site at the 3' end of the 28s sequence and is shown to be a site of rapid rna processing. transcription continues another 235 bp past t1 to site t2, which marks a boundary between relatively stable and highly unstable transcripts. however, t2 does not cause polymerase release. in nuclear run-off experiments transcription is detected across th ... | 1986 | 3453104 |
| dna sequences for typical ribosomal gene spacers from xenopus laevis and xenopus borealis. | | 1987 | 3453114 |
| posttranscriptional regulation of albumin gene expression in xenopus liver: evidence for an estrogen receptor-dependent mechanism. | we have previously shown that estrogen administration to male xenopus laevis results in the posttranscriptional suppression of serum albumin mrna concurrent with the transcriptional activation of the genes for the yolk protein precursor vitellogenin. to determine whether the posttranscriptional regulation of albumin gene expression is mediated through a mechanism involving the high affinity estrogen receptor protein or through a receptor-independent mechanism involving a middle affinity cytoplas ... | 1987 | 3454873 |
| the development of serotonergic raphespinal projections in xenopus laevis. | the development of serotonin-immunoreactive neurons in the central nervous system of xenopus laevis larvae has been studied with special emphasis on the development of the raphe nuclei and raphespinal projections. the first serotonergic neurons were observed in the rostral part of the brain stem at stage 25, only 28 hr after fertilization. by stage 28 some 20 serotonin-immunoreactive neurons were found in the rostral part of the brain stem, bearing small protrusions on the ventromedial side of t ... | 1986 | 3455605 |
| synthetic oligonucleotide tails inhibit in vitro and in vivo translation of sp6 transcripts of maize zein cdna clones. | a maize zein cdna clone was used to synthesize mrna with the sp6 in vitro transcription system. although we obtained full-length transcripts of the cdna sequence, these were inefficient templates for protein synthesis. removal of the 5' oligo(g) sequence that was synthesized during the cdna cloning procedure allowed efficient translation of the mrnas in a wheat germ cell-free protein synthesis system or in xenopus laevis oocytes. the alteration in translational efficiency did not result from an ... | 1986 | 3456558 |
| temporal order of replication of xenopus laevis 5s ribosomal rna genes in somatic cells. | the timing of replication of both the somatic and oocyte-type 5s ribosomal rna genes of xenopus laevis was determined in cultured cells by using 5-bromodeoxyuridine labeling of dna coupled with a retroactive synchrony technique employing the fluorescence-activated cell sorter (facs). the somatic genes replicate very early in s phase, while the oocyte genes replicate very late. these experiments provide direct evidence for a model [gottesfeld, j. & bloomer, l. s. (1982) cell 28, 781-791] in which ... | 1986 | 3458252 |
| replication forks are underrepresented in chromosomal dna of xenopus laevis embryos. | chromosomal dna was isolated from rapidly dividing cells of xenopus laevis embryos at blastulation, at gastrulation, and at the beginning of hatching. few, if any, replication forks were seen by electron microscopy in dna isolated at any stage of embryogenesis. instead, unbranched dna, which appeared to be single-stranded, was abundant at all stages. the percentage of chromosomal dna that was single-stranded was quantitated by electron microscopy and by monitoring the release of acid-soluble rad ... | 1986 | 3461467 |
| identification of estrogen-responsive dna sequences by transient expression experiments in a human breast cancer cell line. | the expression of a hybrid gene formed by the promoter region of the xenopus laevis vitellogenin gene b1 and the cat coding region is regulated by estrogen when the gene is transfected into hormone-responsive mcf-7 cells. furthermore, the 5' flanking region of the gene b1 alone can confer inducibility to heterologous promoters, although to a varying extent depending on the promoter used. deletion mapping of he vitellogenin hormone-responsive sequences revealed that a 13 bp element 5'-agtcactgtga ... | 1986 | 3466137 |
| heat shock stabilizes highly unstable transcripts of the xenopus ribosomal gene spacer. | we have shown recently that, in xenopus laevis oocytes, the 3' end of the longest detectable ribosomal precursor rna is not formed by transcription termination but by rna processing and that rna polymerase i continues to transcribe through the intergenic spacer region. in oocytes, these spacer transcripts are turned over rapidly, and the only apparent transcription termination site is located 215 base pairs upstream of the 5' end of the next transcription unit. in this paper we show that, at hea ... | 1987 | 3467358 |
| expression of size-selected mrna encoding the intestinal na/glucose cotransporter in xenopus laevis oocytes. | the expression of the rabbit intestinal brushborder na/glucose cotransporter has been studied in xenopus oocytes. poly(a)+ rna isolated from the intestinal mucosa was injected into oocytes, and the expression of the transporter in the oocyte plasma membrane was assayed by measuring the na-dependent phlorizin-sensitive uptake of methyl alpha-d-[14c]glucopyranoside (meglc). expression of the glucose carrier was detected 3-7 days after mrna injection, and the rate of glucose transport was proportio ... | 1987 | 3472228 |
| functional gametes derived from explants of single blastomeres containing the "germ plasm" in xenopus laevis: a genetic marker study. | single blastomeres containing the "germ plasm" were isolated from 32-cell embryos of xenopus albino (ap/ap) or wild type and cultured in vitro until the corresponding normal control embryos reached the neurula stage. the resulting explants from albinos were implanted into wild-type host neurulae and vice versa. the formation of functional gametes, eggs or sperm, of donor type was tested when the operated host embryos had reached sexual maturity. the color of the eggs laid by the experimental fem ... | 1987 | 3474188 |
| stable expression of transfected torpedo acetylcholine receptor alpha subunits in mouse fibroblast l cells. | torpedo californica electric organ cdna libraries were constructed in lambda gt10 and lambda gt11. four acetylcholine receptor (acchor) subunit cdna clones were isolated and shown to contain the entire coding region for each of the subunits. when in vitro synthesized acchor mrna was microinjected into xenopus laevis oocytes, functional cell surface acchors were expressed. a very simple and fast 22na-uptake experiment was performed on batches of microinjected oocytes to identify oocytes that were ... | 1987 | 3475714 |
| mouse and frog violate the paradigm of species-specific transcription of ribosomal rna genes. | transcription of ribosomal rna genes by rna polymerase i is generally accepted as being highly species specific, a conclusion based on numerous reports that rrna genes of one species are not transcribed by factors of even closely related species. it thus was striking to find that cloned rdna from the frog xenopus laevis is specifically transcribed in extracts prepared from mouse cells. the data in this paper demonstrate that this heterologous transcription is due to a normal initiation process a ... | 1987 | 3478707 |
| the phosphorylation of nucleoplasmin by casein kinase-2 is resistant to heparin inhibition. | highly purified preparations of casein kinase-2 from the nuclei of xenopus laevis oocytes and from calf thymus can phosphorylate in vitro purified nucleoplasmin from x. laevis oocytes and eggs. the phosphorylation of nucleoplasmin by both kinase preparations is quite insensitive to heparin in contrast with casein phosphorylation which is completely abolished by heparin concentrations above 10 micrograms/ml. however, the phosphorylation of nucleoplasmin and casein are inhibited in a very similar ... | 1987 | 3480242 |
| the estrogen-responsive element as an inducible enhancer: dna sequence requirements and conversion to a glucocorticoid-responsive element. | the estrogen-responsive element (ere) present in the 5'-flanking region of the xenopus laevis vitellogenin (vit) gene b1 has been characterized by transient expression analysis of chimeric vit-tk-cat (chloramphenicol acetyltransferase) gene constructs transfected into the human estrogen-responsive mcf-7 cell line. the vit b1 ere behaves like an inducible enhancer, since it is able to confer estrogen inducibility to the heterologous hsv thymidine kinase (tk) promoter in a relative position- and o ... | 1987 | 3480798 |
| casein kinase ii is a major protein phosphorylating activity in the nuclei of xenopus laevis oocytes. | the nuclei of xenopus laevis oocytes contain kinases capable of phosphorylating endogenous and exogenous proteins using either atp or gtp as phosphoryl donors. these enzymes are much more active with casein and phosvitin as substrates than with histones or protamines. the protein phosphorylating activity of oocyte nuclear extracts is not regulated by cyclic nucleotides, phorbol esters, calmodulin and calcium, or phospholipids. however, the casein phosphorylating activity can be greatly enhanced ... | 1987 | 3483172 |
| maturation of rana temporaria and acipenser stellatus oocytes induced by the cytoplasm of embryos at different cell cycle phases and at different stages of cleavage and blastulation. | experiments involving injections of cytoplasm from the cleaving embryos of rana temporaria and acipenser stellatus into fully grown oocytes of the same species and of xenopus laevis, show that at all mitotic phases, and throughout the period of synchronous cleavage divisions, the cytoplasm is characterized by high activity of the germinal vesicle breakdown factor. this activity decreases during nuclear division desynchronization and drops sharply after the mitotic index fall upon blastulation. a ... | 1986 | 3484433 |
| analysis of hemopoietic lineage of accessory cells in the developing thymus of xenopus laevis. | the developmental history of accessory cells in the thymus was studied by grafting hemopoietic stem cells into cytogenetically distinct frog embryos (diploid-2n or triploid-3n) before the establishment of circulation and overt differentiation and colonization of the thymus. the dna content of cortical thymocytes and circulating erythrocytes was quantified by staining with propidium iodide and measuring the amount of red fluorescence emitted by individual nuclei with the use of flow cytometry. ac ... | 1986 | 3484489 |