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The ribonucleic acid-dependent deoxyribonucleic acid polymerase assay was used to detect type-C viruses in live virus vaccines. Conditions were first established to maximize the sensitivity of the assay. Vaccines tested included live poliomyelitis, rubella, measles, mumps, and yellow fever. Only yellow fever and measles vaccines known to have been produced in avian leukosis-contaminated cells showed evidence of type-C viruses using the assay. The result of the survey show that the assay has direct practical application to the problem of detecting latent agents in biological products intended for human use.
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Yeast poly(adenylic acid)-containing messenger ribonucleic acid isolated from two strains of Saccharomyces cerevisiae was fractionated by preparative polyacrylamide gel electrophoresis in the presence of formamide. Three messenger ribonucleic acids, present at high intracellular concentration, were electrophoretically eluted from the polyacrylamide gels and translated in a wheat germ cell-free extract. The in vitro synthesized polypeptides were identified by tryptic peptide analysis. Messenger ribonucleic acids coding for enolase and glyceraldehyde-3-phosphate dehydrogenase were isolated from commercially grown baker's yeast (strain F1), and messenger ribonucleic acid coding for phosphoglycerate kinase was isolated from Saccharomyces cerevisiae (ATCC 24657). Significant differences in the spectrum of abundant messenger ribonucleic acids isolated from commercially grown baker's yeast (strain F1) and strain 24657 were observed. When both strains were grown under identical conditions, however, the spectrum of messenger ribonucleic acid isolated from the cells is indistinguishable.
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The acid-soluble ribonucleic acid degradation products formed by Escherichia coli cells starved for a carbon source have been identified. They comprise oligonucleotides, nucleoside diphosphates, 5'- and 3'-nucleoside monophosphates, nucleosides, and free bases. The majority of these products are excreted phates, nucleosides, and free bases. The majority of these products are excreted into the medium, and only small and constant amounts are kept in the pool. During carbon starvation at elevated temperatures, mutants deficient in ribonuclease I do not form oligonucleotides and 3'-nucleoside monophosphates, and mutants that contain a modified form of polynucleotide phosphorylase do not accumulate nucleoside diphosphates. 5'-Nucleoside monophosphates do accumulate, however, in a mutant containing thermoabile ribonuclease II, under conditions where more than 95% of all enzyme activity had been destroyed. The data presented confirm the participation of ribonuclease I and polynucleotide phosphorylase in the final steps of ribonucleic acid degradation and indicate that an exonuclease forming 5'-nucleoside monophosphates is also involved.
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Distances were measured by nonradiative energy transfer from fluorescent probes specifically located on one of three points of yeast or Escherichia coli Phe-tRNAPhe enzymatically bound to the entry site or to the acceptor site of E. coli 70S ribosomes to energy-accepting probes on the 3' end of the 16S ribonucleic acid (RNA) of the 30S subunit. The Y base in the anticodon loop of yeast tRNAPhe was replaced by proflavin. Fluorescein isothiocyanate was attached to the X base (position 47) of E. coli tRNAPhe. E. coli tRNAPhe which had been photochemically cross-linked between positions 8 and 13 followed by chemical reduction to form a fluorescent probe was also used. Labeled tRNAs were aminoacylated and enzymatically bound to the ribosome in the presence of elongation factor Tu and guanosine 5'-triphosphate (acceptor-site binding) or a nonhydrolyzable analogue (entry-site binding). Nonradiative energy transfer measurements were made of the distances between fluorophores located on the Phe-tRNA and the fluorophore at the 3' end of 16S RNA. Calculations were based on comparison of the fluorescence lifetime of the energy donor, located on the Phe-tRNA, in the absence and presence of an energy acceptor on the 3' end of the 16S RNA. Under both sets of binding conditions, the distances to the 3' end of 16S RNA were found to be the following: cross-linked tRNA, greater than 69 A; Y base of tRNA, greater than 61 A. The distance between the 3' end of 16S RNA and the X base of tRNA was found to be 81 A under acceptor-site binding conditions but greater than 86 A under entry-site binding conditions.
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S-Adenosylmethionine-dependent ribosomal RNA (rRNA) methylase has been purified approx. 90-fold from rat liver nuclei. The partially purified methylase catalyzes the methylation of base and ribose in hypomethylated nuclear rRNA prepared from the regenerating rat liver after treatment with ethionine and adenine. The enzyme has an apparent molecular weight of about 3 x 10(4) and a sedimentation coefficient of 3.0 S. The enzyme is optimally active at pH 9.5 and sensitive to p-chloromercuribenzoate. Thiol-protecting reagents, such as dithiothreitol, are necessary for its activity, and the enzyme requires no divalent cations for its full activity. This enzyme did not efficiently transfer the methyl group to nuclear rRNA from normal rat liver, compared with hypomethylated nuclear rRNA. Methyl groups were mainly incorporated into pre-rRNA larger than 28 S, and the extent of 2'-O-methylation of ribose by this enzyme was greater than that of base methylation in the hypomethylated rRNA. No other nucleic acids, including transfer RNA (tRNA) and microsomal RNA from normal as well as ethionine-treated rat livers, tRNA from Escherichia coli, yeast RNA, and DNA from rat liver and calf thymus, were significantly methylated by this methylase. These results suggest that partially purified rRNA methylase from rat liver nuclei incorporates methyl groups into hypomethylated pre-rRNA from S-adenosylmethionine.
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A non-steady-state kinetic method has been developed to observe the initiation of long RNA chains by Escherichia coli RNA polymerase without the enzyme turnover. This method was used to determine the order of binding of the first two nucleotides to the enzyme in RNA synthesis with the first two nucleotides to the enzyme in RNA synthesis with poly(dA-dT) as the template. It was shown that initiator [ATP, uridyly(3'-5')adenosine, or adenyly(3'-5')uridylyl-(3'-5')adenosine] binds first to the enzyme-template complex, followed by UTP binding. The concentration dependence of UTP incorporation into the initiation complex suggests that more than one UTP molecule may bind to the enzyme-DNA complex during the initiation process. Comparison of the kinetic parameters derived from these studies with those obtained under steady-state conditions indicates that the steps involving binding of initiator or UTP during initiation cannot be rate limiting in the poly(dA-dT)-directed RNA synthesis. The non-steady-state technique also provides a method for active-site titration of RNA polymerase. The results show that only 36 +/- 9% of the enzyme molecules are active in a RNA polymerase preparation of high purity and specific activity. In addition, the minimal length of poly(dA-dT) involved in RNA synthesis by one RNA polymerase molecule was estimated to be approximately 500 base pairs.