Purification of DNA polymerase δ as an essential Simian virus 40 DNA replication factor

DNA replication from the SV40 origin can be reconstituted in vitro using purified SV40 large T antigen, cellular topoisomerases I and II, replication factor A (RF-A), proliferating cell nuclear antigen (PCNA), replication factor C (RF-C), and a phosphocellulose fraction (IIA) made from human cell extracts (S100). Fraction IIA contains all DNA polymerase activity required for replication in vitro in addition to other factors. A newly identified factor has been purified from fraction IIA. This factor is required for complete reconstitution of SV40 DNA replication and co-purifies with a PCNA-stimulated DNA polymerase activity. This DNA polymerase activity is sensitive to aphidicolin, but is not inhibited by butylanilinodeoxyadenosine triphosphate or by monoclonal antibodies which block synthesis by DNA polymerase a. The polymerase activity is synergistically stimulated by the combination of RF-A, PCNA, and RF-C in an ATP-dependent manner. Purified calf thymus polymerase δ can fully replace the purified factor in DNA replication assays. We conclude that this factor, required for reconstitution of SV40 DNA replication in vitro, corresponds to human DNA polymerase 5.