Structural analysis of the intracellular RNAs of murine mammary tumor virus

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Abstract
Murine mammary tumor virus (MuMTV)-specific RNA was characterized in several types of cells in which viral DNA is transcribed into RNA: cultured GR mouse mammary tumor cells, S49 lymphoma cells from BALB/c mice, lactating mammary glands from C57BL/6 mice and mink lung cells infected in vitro with MuMTV. In all cell types studied, there are 3 distinct species of intracellular viral RNA, with sedimentation coefficients of 35S, 24S and 13S (MW of 3.1 .times. 106, 1.5 .times. 106 and 0.37 .times. 106) as determined by rate-zonal sedimentation in sucrose gradients and by electrophoresis in agarose gels under denaturing conditions. The 3 viral RNA species appear to be present regardless of viral RNA concentration, responsiveness to glucocorticoid hormones, production of extracellular virus and use of either endogenous or acquired MuMTV proviral DNA as template. The 3 viral RNA display characteristics of mRNA: they are polyadenylated, associated with polyribosomes and released from polyribosomes by treatment with EDTA; all 3 species presumably direct the synthesis of virus-coded proteins. The 2 larger species of viral RNA are probably responsible for synthesis of the structural proteins of the virion; the function of the 13S RNA is not known. Both subgenomic RNA contain sequences found at the 3'' terminus of 35S (or genomic) RNA. Only the 24S RNA (not the 13S RNA) contains sequences located at the 5'' terminus of 35S RNA and are apparently transposed during RNA synthesis or maturation, as described for subgenomic mRNA of other retroviruses.