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Three sizes of subunits in RNAs from feline sarcoma-leukaemia virus mixtures.

RNA from the Snyder-Theilen feline sarcoma-leukaemia virus complex (ST-FeSV-FeLV) sedimented in a double-peaked band between 50 and 70S, but Gardner-Arnstein (GA) FeSV-FeLV RNA sedimented in a single 70S peak. FeLV isolated from the ST virus mixture contained RNA which sedimented in a 70S band like GA-FeSV-FeLV RNA, but F422 FeLV RNA sedimented more slowly, at 50 to 60S. After thermal denaturation, resedimentation revealed three classes of RNA subunits in ST-FeSV-FeLV RNA: the first class, 35 to 37S, was also found in ST-FeLV and other FeLVs (except F422 FeLV), in the endogenous feline virus, RD114 and in GA-FeSV-FeLV; the second class, 32 to 34S, was similar to subunits in F422 FeLV and minor components of GA-FeSV-FeLV and ST-FeLV; the third class, 25S, was detected only in ST-FeSV-FeLV RNA. Electrophoresis of RNA species in buffered formamide provided evidence that the three classes of RNA subunits distinguishable on the basis of sedimentation rates actually represent three size classes of subunits. The ST virus mixture was shown to contain about equal titres of infectious FeLV and transforming FeSV whereas GA-FeSV-FeLV had at least a 10-fold excess fo FeLV over FeSV. These observations are discussed in terms of possible origins of the three sizes of FeSV-FeLV RNA subunits and their relationships to three species of FeSV-FeLV proviral DNA described recently (Sherr et al. 1979).