Metabolism of viral RNA in murine leukemia virus-infected cells; evidence for differential stability of viral message and virion precursor RNA.

Molecular hybridization techniques were used to examine the stability of viral message and virion precursor RNA in murine leukemia virus-infected cells treated with actinomycin D. Under the conditions used, viral RNA synthesis was inhibited, but viral protein synthesis continued, and the cells produced noninfectious particles (actinomycin D virions) lacking genomic RNA (J. G. Levin and M. J. Rosenak, Proc. Natl. Acad. Sci. U.S.A. 73:1154-1158, 1976). Analysis of total RNA in virions revealed that the amount of hybridizable viral RNA decreased steadily after the addition of actinomycin D and by 8 h was 10% of the control value. Studies on fractionated viral RNA showed that this low level of hybridization is due to residual 70S RNA in the virion population. The results indicated that viral RNA which is destined to be encapsidated into virions has a half-life of approximately 3 to 4 h. In contrast, other intracellular virus-specific RNA molecules appeared to be quite stable and persisted for a long period of time, with a half-life of at least 12 h. These observations support the idea that two independent functional pools of 35S viral RNA exist within the infected cell: one serving as message and the other as precursor to virion RNA. The existence of two viral RNA pools was further documented by the finding that 12 h after the addition of actinomycin D, when virion precursor RNA was depleted, 35S and 21S viral nRNA species could be identified in polyribosomal RNA as well as in total polyadenylated cell RNA. Surprisingly, 35S and mRNA declined more rapidly than did 21S mRNA, which appeared to be increased in amount.