The synthesis of viral- and cellular-DNA in mammalian cells exposed to polyoma virus

Summary

Various mammalian cell cultures were examined for their ability to support polyoma virus DNA replication, and for induction of cellular DNA synthesis, as a result of infection by polyoma virus. Viral DNA synthesis was measured by the technique of DNA-DNA hybridization which allowed its detection at a level of 0.2% of that occurring during optimum viral DNA replication in mouse cells. All those cultures which failed to produce significant yields of infectious virus were also negative for viral DNA synthesis, indicating that restriction operates at an early stage in the infection cycle; and also were not induced to synthesize cellular DNA. The only exception was the BHK-21 cell line, in which polyoma virus infection stimulated the incorporation of labelled thymidine into DNA, in the absence of detectable viral DNA synthesis. Polyoma transformed hamster cells, known to harbor viral genetic information, were not induced to synthesize viral DNA following a variety of“rescue” attempts, in contrast to cultures of SV 40 (Simian virus 40) — transformed cells in which SV 40 DNA replication could be measured after analogous treatments. Thus in all of the non-murine cultures examined, polyoma virus gene expression was restricted at a stage prior to viral DNA replication.