Simian virus 40 as a probe for studying inducible repair functions in mammalian cells.

We describe the use of Simian Virus 40 (SV40) as a molecular probe for studying the cellular functions induced in cultured monkey kidney cells in response to DNA damaging agents. (a) Ultraviolet (UV) irradiation of SV40-infected cells inhibits viral DNA replication. Replication forks are blocked by the first pyrimidine dimer encountered. In some cases, a single-strand break seems to occur at the level of the dimer inhibiting the fork of replication. This break, which can be visualized by electron microscopy studies, might be the first step in an excision repair pathway. (b) Treatment of monkey kidney cells with acetoxy-acetyl-aminofluorene or UV light before infection with UV-irradiated SV40 induces a mutagenic replication mode, as shown by an increase of the mutation frequency of thermosensitive SV40 mutants. (c) A possible recombination assay using various SV40 mutants infecting the same cell is proposed and discussed.