Intracellular and virion 35 S RNA species of murine sarcoma and leukemia viruses

RNA molecules from the following sources were treated with dimethyl sulfoxide to dissociate noncovalent aggregates and resolved by electrophoresis on polyacrylamide gels: (1) transformed MSV(MLV)-producing Balb/3T3 cells (MSV-39, clone 24), (2) transformed MSV(MLV)-producing rat cells (78A1), (3) MSV transformed, non virus-producing hamster cells (HT-1), (4) MLV-producing Balb/3T3 cells, (5) MLV-producing NIH/3T3 cells (6) 60–70 S RNA from MSV(MLV) virions, and (7) 60–70 S RNA from MLV virions. Virus-specific RNA was detected by hybridization of RNA in gel fractions with the ³H-DNA product of the MSV(MLV) RNA-directed DNA polymerase. Two well defined viral RNA species with sedimentation coefficients of 35 S and 20 S, but none of intermediate size, were detected in both MSV(MLV) producing cell lines. The non virus-producing HT-1 cell line contained a viral RNA species slightly smaller than 35 S, about 33 S, but no detectable 20 S virus-specific RNA. These results with 78A1 and HT-1 cells agree with previous conclusions based on rate-zonal centrifugation in sucrose density gradients (Tsuchida et al., 1972). The two MLV-producing mouse cell lines contained a well defined 35 S RNA peak, a somewhat less pronounced 20 S RNA peak, and heterogeneous RNA species of smaller molecular weights. Although both 35 S and 20 S virus RNA species were detected in cells replicating murine oncornaviruses, labeled 60–70 S RNA isolated from MSV(MLV) virions (consisting mainly of MLV) and MLV virions, and dissociated with dimethyl sulfoxide or by heat, consisted of 35 S RNA and about 10–15% 7 S RNA plus 4–5 RNA, but no detectable 20 S RNA. Hybridization-competition experiments using MSV(MLV) 60–70 S ³H-RNA (consisting mainly of MLV RNA) and saturating amounts of the unlabeled DNA product of the MSV(MLV) RNA-directed DNA polymerase showed that 35 S RNA from cells replicating MSV(MLV) shares virtually all of its nucleotide sequences with MSV(MLV) 70 S RNA; these data suggest that intracellular 35 S RNA species are the major precursors to virion 70 S RNA. In contrast, 33 S RNA from HT-1 cells shares only about 50% of its sequences with MSV(MLV) 70 S RNA indicating that only part of the sequences of MSV(MLV) 60–70 S RNA are integrated and/or transcribed in this non virus-producing MSV transformed cell.