DNA polymerase delta is required for human mismatch repair in vitro.

HeLa nuclear extract was resolved into a depleted fraction incapable of supporting mismatch repair in vitro, and repair activity was restored upon the addition of a purified fraction isolated from HeLa cells by in vitro complementation assay. The highly enriched complementing activity copurified with a DNA polymerase, and the most pure fraction contained DNA polymerase delta but was free of detectable DNA polymerases alpha and epsilon. Calf thymus DNA polymerase delta also fully restored mismatch repair to the depleted extract, indicating DNA polymerase delta is required for mismatch repair in human cells. However, due to the presence of DNA polymerases alpha and epsilon in the depleted extract, potential involvement of one or both of these activities in the reaction cannot be excluded.