All intact subunit RNAs from Rous sarcoma virus contain poly (A).

The capacity of RNA subunits of Schmidt-Ruppin Rous sarcoma virus to bind (dT)n was studied by cesium sulfate density gradient centrifugation, sucrose gradient centrifugation, or polyacrylamide gel electrophoresis. Two classes of subunits were observed. In agreement with previous reports, 60 to 70% of the purified subunits were capable of binding (dT)n. The remaining, nonbinding RNAs, although indistinguishable in size from whole subunits, were shown to be fragments that had lost the (rA)n terminus by random nucleolytic cleavage. This was deduced from the molecular weight distribution of the nonbinding RNAs from high molecular weight RNA. In addition, virtually all subunit RNA from early harvest virus, which contains a greater proportion of intact subunit, binds (dT)n.