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At least 19 recordsLinked to original sources
PubMed1976

Translation of Xenopus liver messenger RNA in Xenopus oocytes: vitellogenin synthesis and conversion to yolk platelet proteins.

Xenopus liver vitellogenin and albumin mRNAs injected into Xenopus oocytes are correctly translated, as shown by specific immunoprecipitation and co-electrophoresis with purified Xenopus vitellogenin (molecular weight 210,000 daltons) and albumin (molecular weight 72,000 daltons). Vitellogenin made in oocytes under the direction of injected liver mRNA is unstable compared to other proteins made on injected messengers (such as albumin and globin) and endogenous oocyte proteins (including actin), the half-life of newly made vitellogenin being about 8 hr. Pulse-chase experiments with 35S-methionine show vitellogenin to be a precursor to yolk platelet lipovitellin (molecular weight 120,000 daltons), while 3H-serine labeling demonstrates conversion to phosvitin (molecular weight 34,000 daltons). In contrast, injected 3H-serine 35S-methionine-labeled Xenopus vitellogenin protein is not converted to yolk platelet proteins and is degraded rather slowly (half-life, 23, 29 hr). Phosphorylation of serine residues in phosvitin can be detected in oocytes injected with 32PO4 or gamma-32P-ATP; thus exogenously derived yolk platelet protein is further modified, or turned over, once it is within the oocyte. Moreover, vitellogenin made in oocytes programed with liver mRNA is phosphorylated. Thus phosphorylation, assembly into yolk platelets, and cleavage are events that do not require vitellogenin supplied by the normal pathoways involved in yolk formation (synthesis and post-translational modification in the liver, transport in the serum, and follicle cell-dependent pinocytosis). Vitellogenin mRNA sediments at about 29S in a sucrose-SDS gradient, while albumin messenger peaks at 16S; both species contain poly(A). These liver mRNAs are functionally stable in oocytes for at least 5 days. Vitellogenin-forming activity, relative to albumin, actin, or total endogenous activity, increases with time, and the final rate of 2-2.5 times the initial rate is only reached 3 days after injection. The potentiation effect probably stems from an increase in the efficiency of translation of vitellogenin mRNA. The availability of homologous mRNAs now permits injected messenger to be used as a valide probe of oocyte function; the biological activity of mRNA from a non-ovarian Xenopus tissue proves that some at least of the translational systems within the Xenopus oocyte are not cell type-specific. Moreover, the whole cell system is eminently suitable for assaying putative translational (and possibly transcriptional) control elements from frog liver.

Albumins↗
PubMed1975

Structural studies of the Xenopus 19S immunoglobulin and 7S immunoglobulin and two immunoglobulin-like proteins.

Xenopus laevis 19S and 7S immunoglobulins (Ig) were extensively reduced and alkylated, their H and L chains spearated and their molecular weights determined. Two kinds of L chains of molecular weight 25,000 and 27,000 were revealed by SDS-polyacrylamide gel electrophoresis. In addition two Ig-like proteins consisting of heavy chains only, of 19S H-type and with similar molecular weight, were detected in Xenopus serum ans isolated. These proteins share common antigenic determinants with Xenopus 19S Ig heavy chains and are devoid of light chain determinants.

Alkylation↗
PubMed1977

Purification of a DNA-binding protein from Xenopus laevis unfertilized eggs.

A DNA-binding protein from Xenopus laevis unfertilized eggs has been purified to apparent homogeneity. It is a heat stable, lysine-rich protein and has a molecular weight corresponding to 8,200 daltons, measured by sodium dodecyl sulphate gel electrophoresis. The protein, which is active in a monomeric form, stimulates DNA polymerase alpha, and binds to single and double stranded DNA. One egg contains about 4 x 10(12) molecules (minimum estimate) of the protein; since we calculate that 4 x 10(8) molecules are sufficient to cover the entire genome (haploid complement), there is much more protein than is needed to cover chromosomal DNA.

Amino Acids↗
PubMed1978

DNAs of simian virus 40 and polyoma direct the synthesis of viral tumor antigens and capsid proteins in Xenopus oocytes.

Purified simian virus 40 and polyoma DNAs injected into nuclei of Xenopus oocytes were transcribed and subsequently translated into virus-specific tumor antigens and capsid proteins. Simian virus 40 large and small tumor antigens synthesized in the oocytes were indistinguishable, by gel electrophoresis and [35S]methionine-labeled tryptic peptide mapping, from the corresponding polypeptides synthesized in CV-1 African green monkey cells. The synthesis of large simian virus 40 tumor antigen implies the correct splicing of its mRNA, which is complementary to nonadjacent nucleotide sequences in the early region of the viral genome. Polyoma DNA directed synthesis of two polyoma tumor antigen polypeptides, 57,000 Mr and small tumor antigen, and of the main capsid protein.

Animals↗
PubMed1977

Discussion paper: induction by progesterone and a "maturation-promoting factor" of soluble proteins in Xenopus laevis oocytes in vitro.

In vitro incubation of isolated X. laevis oocytes with progesterone induces the specific labeling of proteins during maturation. They are detected as several discrete peaks with a double-labeling technique that involves the injection of [3H] leucine into hormone-treated and [14C] leucine into control cells. The peaks are separated by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Identical proteins are obtained with two other steroids that provoke maturation and with p-chloromercuribenzoate. The same progesterone-induced proteins are observed even if oocytes have been treated with actinomycin D or ethidium bromide or have been enucleated. Cycloheximide suppresses the labeling of proteins that are induced by progesterone, if administered either at the time of radioactive amino acid exposure or after prelabeling the oocytes to determine whether the hormone-induced peaks are due to compartmental changes of the proteins. A cytoplasmic fraction, obtained from maturing oocytes before GVBD, promotes maturation when injected into resting oocytes and therefore contains an MPF. After this injection, GVBD occurs earlier than during incubation with progesterone and is accompanied by the formation of the same proteins and of MPF, both suppressed by cycloheximide. The possibility that MPF is an induced protein is then discussed. It has been also found that there is a decrease in membrane permeability, as evidenced by decreased leucine uptake into proteins of oocytes incubated in radioactive amino acids and exposed to progesterone. The same decrease occurs after injection of MPF-containing cytoplasm into oocytes.

4-Chloromercuribenzenesulfonate↗
PubMed1978

[Properties of sex steroid-binding protein from Xenopus laevis blood serum and detection of an estradiol-binding component in frog liver cytosol which differs from sex steroid-binding protein].

Binding and physico-chemical properties of sex steroid-binding protein (SBP) from blood serum and those of estrogen-binding components from liver cytosol of pubertal male and female species of clawed frog Xenopus laevis were studied. It was shown that SBP from both sex species of X. laevis specifically binds estradiol (E2) (Ka=5 . 10(6) M-1). Concentration of SBP binding sites for E2 is 7 . 10(-12) mole per mg of protein. Testosterone 5alpha-dihydrotestosterone and E2 effectively compete with [3H]-E2 for SBP binding sites. Hexestrol, progesterone and corticosterone are weak competitors; estrone and E2-17-hemisuccinate do not compete at all. The Strokes radius of SBP is 4.4 nm; sedimentation coefficient is 4.6S. Molecular weight of SBP is 88000; f/f0 is 1.5 SBP from male frog sera has been purified 8.6-fold with 13% yield. Gel-filtration of [3H]-E2 complexes with liver cytosol proteins shows that the livers of male and female frog X. laevis consol proteins shows that the livers of male and female frog X. laevis contain very low amounts of macromolecular component, which specifically binds E2; this component differs from serum SBP in size and in hormonal specificity. It is assumed that this component is a receptor for estrogens.

Animals↗
PubMed1979

Changes in protein synthesis during the development of Xenopus laevis.

Patterns of protein synthesis during the development of Xenopus were studied by two-dimensional gel electrophoresis. Up to the end of the blastula stage we find no newly synthesized proteins which are not already made in the oocyte. The first new proteins are seen during gastrulation, and they increase in number during neurulation. Some of these are restricted to the 'ectodermal' region, and some to the 'endodermal' region of embryos divided into two parts. These new, region-specific proteins include alpha-actin. When the oocyte matures the number of detectable newly synthesized proteins decreases, reaching a minimum in the unfertilized egg. Some, such as beta- and gamma-actin, re-appear at the end of cleavage. This could not be shown to be a recovery artifact. The relation of the total mRNA to these changes in protein synthesis was studied by translation in the lysed reticulocyte cell-free system. The mRNAs that code for oocyte proteins that cease synthesis in the unfertilized egg and re-appear in blastulae are nevertheless detectable in total RNA made from eggs. These proteins therefore seem to cease and resume synthesis through translational control. mRNAs for new proteins first appear after gastrulation, just when these proteins are first detected in vivo. This strongly suggests, though it does not prove, that new gene activity is involved. It is therefore likely that region-specific gene activity is already present by the gastrula stage of development, and has an impact on the most abundant kinds of proteins made in the embryo.

Actins↗