| 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 δ that is required for efficient replication of DNA containing the SV40 origin of replication. PCNA-dependent DNA polymerase δ on a DNA singly primed ∅X174 single-stranded circular 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 δ, in contrast to DAN polymerase α, hardly used RNA-primed DNA templates. These results indicate that both DNA polymerase α and δ are involved in SV40 DNA replication in vitro and their activity depends on PCNA, the elongation inhibitor, and activator I. |
