Minor Base Composition of “70S-Associated” 4S RNA from Avian Myeloblastosis Virus

180

The enzymatic transcription of DNA from the 70S RNA of Rous sarcoma virus (RSV) is initiated on the 3' terminus of a molecule of 4S RNA which is hydrogen bonded to the viral genome. We labeled this primer with radioactive deoxynucleotides, and demonstrated that its release from 70S RNA by thermal denaturation was accompanied by a reduction in the template activity of the viral RNA. Two-dimensional electrophoresis in polyacrylamide gels separated the 4S RNAs associated with the 70S RNA of RSV into approximately eight fractions, each of which appeared to contain a discrete species of tRNA. The RNA in one of these fractions served as the principal primer for initiation of DNA synthesis by both detergent-disrupted virions of RSV and purified RNA-directed DNA polymerase with RSV 70S RNA as template.

mentioning

confidence: 99%

Transcription of DNA from the 70 S RNA of Rous Sarcoma Virus I. Identification of a Specific 4 S RNA Which Serves as Primer

Dahlberg

Sawyer

Taylor

et al. 1974

180

“…Some discrete molecules, such as 7S, 5S, and transfer RNAs are quite likely cellular in origin (4,16,21,23,25); they may have specific functions, or they may be included in the virions upon budding, with no precise function. Virion transfer RNAs are capable of undergoing aminoacylation in vitro (9,13,26,(29)(30)(31). One of the small RNAs can serve as a primer for RNA-directed DNA synthesis (5, 8; A. J. Faras, J. M. Taylor, W. E. Levinson, H. M. Goodman, and J. M. Bishop, J. Mol.…”

mentioning

confidence: 99%

Small RNAs of Rous Sarcoma Virus: Characterization by Two-Dimensional Polyacrylamide Gel Electrophoresis and Fingerprint Analysis

Sawyer

Dahlberg

1973

119

Approximately 15 to 20 different species of small (4 to 7S) RNAs have been purified by two-dimensional polyacrylamide gel electrophoresis of RNA isolated from virions of Schmidt-Ruppin D strain of Rous sarcoma virus. Each species of small RNA has been isolated free of 70S RNA; nine of them, including 5S and 7S RNAs, were also found associated with the 70S genomic RNA. Most of the 4S RNAs are present at an average of less than one copy per virion. The 4S RNAs have Ti RNase (EC 2.7.7.26) fingerprints, which are very similar to those of tRNAs. One of the smallest 4S RNAs, which can act as a primer for initiation of RNA-directed DNA synthesis, is associated with the 70S RNA in 1 to 2 copies per complex, whereas an additional 6 to 8 copies of this molecule are free. MATERIALS AND METHODS Preparation of 32P-labeled RNA. Cultures of chicken embryo fibroblasts (negative for avian leukosis virus group-specific antigen and RNA, and for chicken helper factor; E. Humphries and H. M.

“…Some investigators have found 4S RNA species associated with the 60-70S RNA complex of RNA tumor viruses (4,8), and a recent study of modified nucleic acid bases suggests that associated 4S RNA is very similar in composition to free 4S RNA in avian myeloblastosis virus (AMV) (18). However, this is not resolved, since other investigators do not find 4S RNA molecules associated with the 60-70S RNA complex of closely related avian oncornaviruses (1,19).…”

mentioning

confidence: 99%

Chromatographic Analyses of Isoaccepting tRNAs from Avian Myeloblastosis Virus

Gallagher

Gallo

1973

Avian myeloblastosis virus (AMV) 4S RNA was tested for amino acid acceptor activity for 18 of the 20 amino acids. A nonrandom distribution of viral tRNAs was found compared with tRNA from normal liver or from AMV-infected leukemic myeloblasts, confirming previous reports. Methionine and proline tRNAs were considerably enriched, whereas glutamic acid, glutamine, serine, tyrosine, and valine tRNAs were markedly depleted in AMV relative to homologous cellular tRNAs. The seven AMV tRNAs with the greatest amino acid acceptance capacities, which were in order methionine, proline, lysine, arginine, histidine, isoleucine, and threonine tRNAs, were compared with homologous tRNAs from leukemic myeloblasts and liver by reversed-phase 5 chromatography. Of the 25 isoaccepting chromatographic fractions identified, no tRNA species unique to AMV was detected. Only methionyl-tRNA showed a substantial quantitative variation in isoaccepting species compared with the host cell. Thus, viral selectivity for amino acid-specific tRNAs is not, generally, paralleled by selectivity for individual isoaccepting tRNA species. Qualitative differences in arginyland histidyl-tRNA isoaccepting species were discovered in virus and leukemic myeloblasts compared with liver. This indicates the existence of structural differences in these tRNA species which could be related to virus replication or expression.