Elongation of DNA complementary to the 5' end of the avian sarcoma virus genome by the virion-associated RNA-dependent DNA polymerase

Abstract

RNA-dependent DNA synthesis in a virion-associated reaction has been described as being dependent upon the detergent concentration used for disruption of the virion. In this study, the Triton X-100 concentration was found to affect the elongation of the initially synthesized DNA complementary to the last approximately 100 nucleotides at the 5' end of the RNA (cDNA100). Whereas elongation of cDNA100 increased with time of incubation at the optimal detergent concentration, this process was retarded at higher detergent concentrations. At the optimal detergent concentration, elongated DNA was of low chemical complexity, indicating that extension of cDNA100 occurred at a unique site on the RNA. Higher than optimal detergent concentrations resulted in nonspecific elongation and in DNA of high chemical complexity. This was shown by oligopyrimidine tract analysis. Furthermore, actinomycin D was observed to inhibit the elongation of cDNA100 at the optimal detergent concentration. The nature of the elongation process was elucidated by analysis of DNA synthesized in a virion-associated reaction in the presence of bacteriophage Qbeta RNA. At the optimal detergent concentration DNA complementary only to avian sarcoma virus RNA was synthesized, whereas at higher concentrations DNA was copied from both avian sarcoma virus and Qbeta RNA. We conclude that the elongation mechanism of cDNA100 is affected by the detergent concentration and elongation is unspecific at higher than optimal detergent concentrations. The mechanism by which the nonionic detergent stimulates DNA synthesis has not yet been resolve. We assume that other factors in addition to DNA polymerase are involved in elongation of cDNA100.