The Human Tim/Tipin Complex Directly Interacts with DNA Polymerase {epsilon} 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. Herein, we present evidence that the recombinant human Tim/Tipin complex (and Tim alone) markedly enhances the synthetic activity of DNA polymerase ε. In contrast, no significant effect on the synthetic ability of human DNA polymerase α and δ by Tim/Tipin was observed. Surface plasmon resonance measurements and co-immunoprecipitation experiments revealed that recombinant DNA polymerase ε 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 ε bound to a 40-/80-mer DNA ligand. Our results are discussed in view of the molecular dynamics at the human DNA replication fork.