Role of subunits of 60 to 70S avian tumor virus ribonucleic acid in its template activity for the viral deoxyribonucleic acid polymerase

Heating the 60 to 70 S ribonucleic acid (RNA) of Rous sarcoma virus (RSV) destroys both its subunit structure and its high template activity for RSV deoxyribonucleic acid (DNA) polymerase. In comparative analyses, it was found that the template activity of the RNA has a thermal transition of 70 C, whereas the 60 to 70 S structure dissociates into 30 to 40 S and several distinct small subunits with a T m of 55 C. Analysis by velocity sedimentation and isopycnic centrifugation of the primary DNA product obtained by incubation of 60 to 70 S RSV RNA with RSV DNA polymerase indicated that most, but perhaps not all, DNA was linked to small (S ) RSV RNA primer. Sixty percent of the high template activity of 60 to 70 S RSV RNA lost after heat dissociation could be recovered by incubation of the total RNA under annealing conditions. The template activity of purified 30 to 40 S subunits isolated from 60 to 70 S RSV RNA was not enhanced significantly by annealing. However, in the presence of small (S ) subunits also isolated from 60 to 70 S RNA, the template activity of 30 to 40 S RNA subunits was increased to the same level as that of reannealed total 60 to 70 S RNA. It was concluded that neither the 30 to 40 S subunits nor most of the 4 S subunits of 60 to 70 S RSV RNA contribute much as primers to the template activity of 60 to 70 S RSV RNA. The predominant primer molecule appears to be a minor component of the S subunit fraction of 60 to 70 S RSV RNA. Its electrophoretic mobility is similar to, and its dissociation temperature from 60 to 70 S RSV RNA is higher than that of the bulk of 60 to 70 S RSV RNA-associated 4 S RNA. The role of primers in DNA synthesis by RSV DNA polymerase is discussed.