The Kinetics of Synthesis of Infectious Unintegrated Virus DNA in Rous Sarcoma Virus Infected Chicken Cells

Infectious virus nucleic acids were extracted from the Hirt supernatant of chicken embryo fibroblasts infected for different times with the Schmidt-Ruppin strain of Rous sarcoma virus (RSV). Infectious DNA and DNA-RNA hybrid molecules could be recovered from 6 h after infection in experiments using 1.5 x 10⁹ infected cells. Only small amounts of infectious virus DNA could be purified 6 h after infection whereas at 24 h approximately one infectious DNA molecule could be recovered for each input virus infectious unit. At 24 h, both infectious supercoiled and non-supercoiled molecules were found. The specific infectivity of the supercoiled fraction was less than that of the non-supercoiled fraction. Infectious supercoiled DNA could be recovered from 16 h after infection. Evidence is presented that both forms of unintegrated virus DNA may rest unintegrated for at least 8 days in the cell, though chronically infected cells were shown to contain less than one unintegrated molecule per 10² to 10³ cells.