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The poly(A) sequence of 30 to 40 S Rous sarcoma virus RNA, prepared by digestion of the RNA with RNase T 1 , showed a rather homogenous electrophoretic distribution in formamide-polyacrylamide gels. Its size was estimated to be about 200 AMP residues. The poly(A) appears to be located at or near the 3′ end of the 30 to 40 S RNA because: (i) it contained one adenosine per 180 AMP residues, and because (ii) incubation of 30 to 40 S RNA with bacterial RNase H in the presence of poly(dT) removed its poly(A) without significantly affecting its hydrodynamic or electrophoretic properties in denaturing solvents. The viral 60 to 70 S RNA complex was found to consist of 30 to 40 S subunits both with (65%) and without (approximately 30%) poly(A). The heteropolymeric sequences of these two species of 30 to 40 S subunits have the same RNase T 1 -resistant oligonucleotide composition. Some, perhaps all, RNase T 1 -resistant oligonucleotides of 30 to 40 S Rous sarcoma virus RNA appear to have a unique location relative to the poly(A) sequence, because the complexity of poly(A)-tagged fragments of 30 to 40 S RNA decreased with decreasing size of the fragment. Two RNase T 1 -resistant oligonucleotides which distinguish sarcoma virus Prague B RNA from that of a transformation-defective deletion mutant of the same virus appear to be associated with an 11 S poly(A)-tagged fragment of Prague B RNA. Thus RNA sequences concerned with cell transformation seem to be located within 5 to 10% of the 3′ terminus of Prague B RNA.

Kirsten murine sarcoma-leukemia virus (Ki-MSV[MLV]) was found to contain less RNase H per unit of viral DNA polymerase than avian Rous sarcoma virus (RSV). Upon purification by chromatography on Sephadex G-200 and subsequent glycerol gradient sedimentation the avian DNA polymerase was obtained in association with a constant amount of RNase H. By contrast, equally purified DNA polymerase of Ki-MSV(MLV) and Moloney [Mo-MSV(MLV)] lacked detectable RNase H if assayed with two homopolymer and phage fd DNA-RNA hybrids as substrates. On the basis of picomoles of nucleotides turned over, the ratio of RNase H to purified avian DNA polymerase was 1:20 and that of RNase H to purified murine DNA polymerase ranged between