Polyadenylated virus-specific RNA in baby hamster kidney cells, transformed by polyoma virus

RNA from a clone of polyoma virus-transformed hamster cells was fractionated by chromatography on oligo(dT)-cellulose. The proportion of virus-specific RNA in the polyadenylated and non-polyadenylated fractions was determined by hybridization of the labelled RNA with excess purified polyoma DNA, immobilized on filters. Seventy to 80% of the virus-specific RNA in both polysomal and total cell RNA was found in the polyadenylated fraction. Since it has been shown previously that more than 65% of the total virus-specific RNA is restricted to the nucleus in this cell line, these results indicate that a high proportion (at least 53%) of the nuclear virus-specific RNA is polyadenylated. The sedimentation profile of total polyadenylated virus-specific RNA in dimethyl sulphoxide was comprised mainly of a broad band with a median sedimentation coefficient about 26S (relative to 28S rRNA). This profile was similar to that of total nuclear, and not cytoplasmic, virus-specific RNA. To estimate the intramolecular proximity of virus-specific sequences to poly(A), total RNA was subjected to limited thermal scission to an average mol. wt. similar to that of mRNA. The RNA remaining attached to poly(A) was then isolated, using oligo(dT)-cellulose. It was found that 65% of the virus-specific RNA that was originally attached to poly(A) was released by the thermal scission. Most of the virus-specific sequence within polyadenylated RNA molecules therefore must have been located at some distance from the polyadenylated 3'-terminus. This observation, together with the results of sedimentation analysis, can most simply be explained by postulating the existence of 'hybrid' RNA molecules containing a host-specified sequence located between a virus-specific sequence and the 3'-terminal poly(A).