Requirement for two DNA polymerases in the replication of simian virus 40 DNA in vitro

DNA polymerase α-primase has long been considered the primary, if not sole, replicative DNA polymerase in eukaryotic cells. However, recent experiments have provided indirect evidence that a second DNA polymerase may play a role in DNA replication. To identify cellular proteins necessary for DNA synthesis in mammalian cells, we have been studying the cell-free system developed for the replication of simian virus 40 DNA. In this report, we present direct evidence that a second DNA polymerase is required in addition to DNA polymerase α-primase complex to obtain efficient replication of simian virus 40 origin-containing DNA. This DNA polymerase activity is not affected by monoclonal antibodies that inhibit the activity of DNA polymerase α and is relatively resistant to the inhibitor [N²-(p-n-butylphenyl)-9-(2-deoxy-β-D-ribofuranosyl)guanine 5'-triphosphate]. Moreover, the activity of the polymerase is highly dependent upon the accessory protein, proliferating-cell nuclear antigen. These characteristics are consistent with the hypothesis that this second DNA polymerase is DNA polymerase δ.