Localization of DNA polymerases η and ι to the replication machinery is tightly co-ordinated in human cells

Y-family DNA polymerases can replicate past a variety of damaged bases in vitro but, with the exception of DNA polymerase η (polη), which is defective in xeroderma pigmentosum variants, there is little information on the functions of these polymerases in vivo. Here, we show that DNA polymerase ι (polι), like polη, associates with the replication machinery and accumulates at stalled replication forks following DNA-damaging treatment. We show that polη and polι foci form with identical kinetics and spatial distributions, suggesting that localization of these two polymerases is tightly co-ordinated within the nucleus. Furthermore, localization of polι in replication foci is largely dependent on the presence of polη. Using several different approaches, we demonstrate that polη and polι interact with each other physically and that the C-terminal 224 amino acids of polι are sufficient for both the interaction with polη and accumulation in replication foci. Our results provide strong evidence that polη targets polι to the replication machinery, where it may play a general role in maintaining genome integrity as well as participating in translesion DNA synthesis.