Activation of polyomavirus DNA replication by yeast GAL4 is dependent on its transcriptional activation domains

The polyomavirus replication origin contains transcriptional regulatory sequences. To determine how these elements function in DNA replication, and to learn whether a common mechanism underlies the activation of transcription and DNA replication, we tested whether a well-characterized transcriptional activator, yeast GAL4, was capable of stimulating DNA replication and transcription in the same mammalian cell line. We observed that GAL4 activated polyomavirus DNA replication in mouse cells when its binding site was juxtaposed to the late border of the polyomavirus origin core. Synergistic activation of DNA replication was achieved by multimerization of the GAL4 binding site. Analysis of GAL4 mutant proteins, GAL4 hybrid proteins and mutants of the latter revealed that the activation domains of these transcriptional activators were required to stimulate DNA replication. In agreement with previously published data, the activation domains of GAL4 were also required to enhance transcription in the same mouse cell line. These observations implicate transcriptional activators in Py DNA replication and suggest that similar mechanisms govern the activation of transcription and DNA replication.