SIMIAN-VIRUS-40 SMALL-T ANTIGEN STIMULATES VIRAL-DNA REPLICATION IN PERMISSIVE MONKEY CELLS

The simian virus 40 (SV40) large-T antigen is essential for SV40 DNA r eplication and for late viral gene expression, but the role of the SV4 0 small-t antigen in these processes is still unclear. We have previou sly demonstrated that small t inhibits SV40 DNA replication in vitro. In this study, we investigated the effect of small t on SV40 replicati on in cultured cells. CV1 monkey cell infection experiments indicated that mutant viruses that lack small t replicate less efficiently than the wild-type; virus. We next microinjected CV1 cells with SV40 DNA wi th and without purified small-t protein and analyzed viral DNA replica tion efficiency by Southern blotting. Replication of either wild-type SV40 or small-t deletion mutant DNA was increased three- to fivefold i n cells coinjected with purified small t. Thus, in contrast to our in vitro observation, small t stimulated viral DNA replication in vivo. T his result suggests that small t has cellular effects that are not det ectable in a reconstituted in vitro replication system. We also found that small t stimulated progression of permissive monkey cells-but not of nonpermissive rodent cells-from G(0)-G(1) to the S phase of the ce ll cycle, possibly leading to an optimal intracellular environment for viral replication.