Cis-acting negative control of DNA replication in eukaryotic cells.

We show that in stable monkey cell lines, the replication of a chimeric SV40-BPV episomal replicon occurs once and only once per cell cycle. The copy number of this episome is stably maintained even when an excess of the limiting initiation factor T antigen is provided. These experiments therefore uncover a cis-acting negative control mechanism whereby replication control is not focused on limiting the activity of positive factors; rather, replication is permitted in unreplicated replicons but is actively prevented, in cis, in replicons that have already been duplicated. We also find that the initiation factor SV40 T antigen remains associated with its SV-BPV episomal template in a kinetically stable and potentially heritable state.