Alterations in macromolecular synthesis and cellular growth in mouse embryo fibroblasts infected with friend leukemia virus

The rate of DNA synthesis in secondary mouse embryo fibroblast (MEF‐2) cultures was increased following infection with Friend leukemai virus (FLV) as compared to control cultures which were untreated or exposed to heat‐denatured virus. A peak was reached between 24 and 48 h after infection. Radioautographic studies revealed that the infected cultures had a higher percentage of cells which incorporated tritiated thymidine into their nuclei as compared to controls. This increase was apparently independent of the ability of the cells to divide, since it was also observed in infected stationary cultures. The rates of cellular RNA and protein synthesis did not appear to be affected by FLV infection. The time required for the cell population to double was one‐third shorter in FLV‐infected cultures as compared to controls. The shortening of the generation time was found to be due to a decrease in the time required for the cells to traverse the G1 and S phases of the cell cycle. In addition, after 72 h of growth, the infected cultures reached greater population densities than did either of the controls.