Reinitiation of cellular DNA synthesis in BrdU‐selected nondividing senescent WI‐38 cells by simian virus 40 infection

Bromodeoxyuridine-selected nondividing senescent WI-38 cells were stimulated to synthesize DNA, as evidenced by incorporation of [3H]thymidine into nuclei of senescent cells, after infection with simian virus 40 (SV40). Cellular DNA synthesis was confirmed by DNA-DNA hybridization experiments and the use of temperature-sensitive A gene mutants. The DNA synthesis was, at least in part, semiconservative, as microdensitometry of Feulgen-stained nuclei revealed increased DNA content in a large fraction of the cells in the infected population. Thus, senescent cells retain the capacity to replicate their DNA, despite their intrinsic inability to initiate DNA synthesis.