The Human Tim-Tipin Complex Interacts Directly with DNA Polymerase ϵ and Stimulates Its Synthetic Activity

The Tim-Tipin complex plays an important role in the S phase checkpoint and replication fork stability in metazoans, but the molecular mechanism underlying its biological function is poorly understood. Here, we present evidence that the recombinant human Tim-Tipin complex (and Tim alone) markedly enhances the synthetic activity of DNA polymerase epsilon. In contrast, no significant effect on the synthetic ability of human DNA polymerase alpha and delta by Tim-Tipin was observed. Surface plasmon resonance measurements and co-immunoprecipitation experiments revealed that recombinant DNA polymerase epsilon directly interacts with either Tim or Tipin. In addition, the results of DNA band shift assays suggest that the Tim-Tipin complex (or Tim alone) is able to associate with DNA polymerase epsilon bound to a 40-/80-mer DNA ligand. Our results are discussed in view of the molecular dynamics at the human DNA replication fork.