Studies on the fixation and development of cellular transformation by Rous sarcoma virus

Abstract

The requirement for DNA synthesis in transformation of cells by Rous sarcoma virus (RSV) was confirmed using a nontoxic inhibitor, thymidine (20 m M). Inhibition of DNA synthesis for a 12-hour period immediately after exposure of cells to RSV prevented subsequent transformation. Similar inhibition of DNA synthesis immediately prior to RSV or after a 12-hour delay had little effect on the number of resulting transformed foci. When DNA synthesis was continuously inhibited beginning 12 hours after RSV, morphological transformation developed in the absence of cellular divisions, and transformed loci were comprised of two cells or single cells. Experiments using mitotically synchronized cells demonstrated that both daughter cells of an initially infected cell became transformed. The results demonstrate that there is a fixation period for transformation by RSV requiring DNA synthesis, that the viral genome is duplicated within a single cellular generation and distributed to both cellular progeny at division, and that transformation, once fixed, can develop in the absence of DNA synthesis.