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Biomedical subjects

J R Warner

Publications and source records attributed to J R Warner.

At least 109 records · Page 6Linked to original sources
PubMed1976

Methylated, blocked 5' termini of yeast mRNA.

mRNAs of the yeast, Saccharomyces cerevisiae, have modified 5' termini similar but not identical with those present in the higher eukaryotes. Poly(A)-containing RNA isolated from spheroplasts or from polysomes of cells labeled with [methyl-3H]methoionine or 32Pi contain methylated, blocked 5'-terminal structures of composition: m7G(5')pppAp and m7G(5')pppGp, occurring in a relative distribution of 75% and 25%, respectively. Furthermore there is no N6-methyladenosine nor any other methylated nucleoside in the entire molecule of poly(A)-containing RNA. Experiments with a mutant, temperature-sensitive for the transport of mRNA to cytoplasm, suggest that the methylation and addition of the blocking group take place in the nucleus and that the genetic lesion in the mutant does not affect these mechanisms.

Methionine↗
PubMed1976

The ribosomal proteins of Saccharomyces cerevisiae. Phosphorylated and exchangeable proteins.

Sixty-seven ribosomal proteins of the yeast Saccharomyces cerevisiae have been distinguished by two-dimensional polyacrylamide gel electrophoresis. Five of the ribosomal proteins are phosphorylated in vivo. One of the phosphorylated proteins appears to correspond to the phosphorylated ribosomal protein, S6, of rat liver. Another of the yeast-phosphorylated proteins, which is highly acidic, may be related to the protein L7/L12 of Escherichia coli. The phosphorylation of four of the five ribosomal proteins depends on protein synthesis. Ribosome synthesis, however, is not necessary for the phosphorylation of any of them. Three proteins of the 60 S ribosomal subunit are "exchangeable" in vivo. Two of these are phosphoproteins, one of which is the very acidic protein possibly related to L7/L12 of E. coli. The possible significance of this phosphorylated, exchangeable protein in protein synthesis is discussed.

Animals↗
PubMed1976

Coordinate regulation of the synthesis of eukaryotic ribosomal proteins.

We have developed a method of r the direct measurement, in eukaryotic cells, of the synthesis of ribosomal proteins, irrespective of the synthesis of ribosomes. In this way the synthesis of ribosomal proteins has been examined in mutant strains of Saccharomyces cerevisiae, which are unable to synthesize ribosomes under nonpermissive conditions. The results suggest that the synthesis of more than 40 ribosomal proteins is under coordinate control. Under nonpermissive conditions,the synthesis of each h protein declines exponentially to a basal level which is 10-20% fo normal. The kinetics of that decline suggest that an early, if not primary, result of the nonpermissive conditions is the cessation of production of new mRNA for eac of the ribosomal proteins. The coordinate regulation appears not to be influenced directly by the rate of transcription of ribosomal precursor RNA.

Adipose Tissue↗
PubMed1976

Kinetics of labeling of the S-adenosylmethionine pool of Saccharomyces cerevisiae.

A method has been developed for studying the specific activity of the pool of S-adenosylmethionine in yeast. The pool reaches half-maximal specific activity within 30 s after the addition of [methyl-3H]methionine. After addition of an excess of nonradioactive methionine, the specific activity of S-adenosylmethionine is reduced by half within 20 s. During that period there is a substantial expansion of the pool. A logarithmically growing cell in synthetic medium contains about 2 X 10(6) molecules of S-adenosylmethionine, of which only 10% is used for the methylation of ribonucleic acid molecules.

Adenine↗
PubMed1971

Ribosome formation is blocked by camptothecin, a reversible inhibitor of RNA synthesis.

A new drug, camptothecin, has been used to study the regulation of ribosome synthesis in HeLa cells. 5 muM camptothecin inhibits the synthesis of heterogeneously sedimenting nuclear RNA by about 70%. Camptothecin also blocks a specific step in the processing of ribosomal precursor RNA, allowing the conversion of 45S RNA to 32S RNA, but inhibiting the conversion of 32S RNA to 28S RNA. The action of camptothecin, unlike that of actinomycin D, is rapidly reversible. Within 5 min after the removal of the drug, ribosomal precursor RNA synthesis and maturation resume at the normal rate. Ribosomal proteins made in the presence of camptothecin do not accumulate in the nucleolus, and are not subsequently used to form ribosomes if RNA synthesis is allowed to resume.

Alkaloids↗
PubMed1971

Cytoplasmic synthesis of nuclear proteins. Kinetics of accumulation of radioactive proteins in various cell fractions after brief pulses.

The synthesis of cytoplasmic and nuclear proteins has been studied in HeLa cells by examining the amount of radioactive protein appearing in the various subcellular fractions after labeling for brief periods. Due to the rapid equilibration of the amino acid pool, the total radioactivity in cytoplasmic protein increases linearly. The radioactivity observed in the cytoplasm is the sum of two components, the nascent proteins on the ribosomes and the completed proteins. At very short labeling times the specific activity of newly formed proteins found in the soluble supernatant fraction (completed protein) increases as the square of time, whereas the specific activity of the ribosomal fraction (nascent protein) reaches a plateau after 100 sec. The kinetics of accumulation of radioactive protein in the nucleus and the nucleolus is very similar to that of completed cytoplasmic protein, which suggests that the proteins are of similar origin. The rate of release and migration of proteins from the ribosomes into the nucleus requires less time than the synthesis of a polypeptide, which is about 80 sec. The uptake of label into nucleolar proteins is as rapid as the uptake of label into proteins of the soluble fraction of the cytoplasm, while nuclear proteins, including histones, tend to be labeled more slowly. The same results are obtained if protein synthesis is slowed with low concentrations of cycloheximide. The kinetics of incorporation of amino acids into various fractions of the cell indicates that the nucleus and the nucleolus contain few if any growing polypeptide chains, and thus do not synthesize their own proteins.

Analysis of Variance↗
PubMed1971

Small ribosomal ribonucleic acid species of Saccharomyces cerevisiae.

Yeast ribosomes contain two small molecular-weight species of ribonucleic acid (RNA), in addition to transiently associated transfer RNA. The 5S RNA species is part of the large ribosomal subunit and appears to be exactly the same size as 5S RNA from other organisms. There is another RNA molecule, approximately 5.8S or 150 nucleotides in size, which is noncovalently attached to the 25S ribosomal RNA and can be freed by gentle heating or urea treatment. Neither 5 nor 5.8S RNA are methylated. The 5.8S RNA is probably derived from a part of the 35S precursor RNA, whereas the 5S RNA is made de novo. These results substantiate the notion that ribosome biosynthesis in yeast is analogous to that of the higher eukaryotes.

Acrylates↗