Mouse p53 blocks SV40 DNA replication in vitro and downregulates T antigen DNA helicase activity.

Immunopurified mouse p53 proteins were used to gain experimental access to the mechanisms underlying nonprimate p53 directed suppression of SV40 origin directed DNA replication in vivo. In replication competent HeLa cell extracts containing exogenous T antigen, mouse p53 blocks T antigen dependent DNA synthesis as in vivo. However, in transcription competent HeLa extracts, mouse p53 has no effect either on overall transcription or on the ability of immunopurified T antigen to downregulate SV40 early transcription. We show that although mouse p53 has no significant effect on T antigen encoded activities such as ATPase and DNA binding, helicase activity is somewhat reduced suggesting that the in vivo suppression by mouse p53 of SV40 replication may be due, at least in part, to direct modulation of T antigen function.