Synthesis of DNA containing the simian virus 40 origin of replication by the combined action of DNA polymerases alpha and delta.

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Abstract
Proliferating-cell nuclear antigen (PCNA) mediates the replication of simian virus 40 (SV40) DNA by reversing the effects of a protein that inhibits the elongation reaction. Two other protein fractions, activator I, and activator II, were also shown to play important roles in this process. We report that activator II isolated from HeLa cell extracts is a PCNA-dependent DNA polymerase .delta. that is required for efficient replication of DNA containing the SV40 origin of replication. PCNA-dependent DNA polymerase .delta. on a DNA singly primed .vphi.X174 single-strained cirucular DNA template required PCNA, a complex of the elongation inhibitor and activator I, and the single stranded DNA-binding protein essential for SV40 DNA replication. DNA polymerase .delta., in contrast to DNA polymerase .alpha., hardly used RNA-primed DNA templates. These results indicate that both DNA polymerase .alpha. and .delta. are involved in SV40 DNA replication in vitro and their activity depends on PCNA, the elongation inhibitor, and activator I.