Localisation of human Y-family DNA polymerase kappa: relationship to PCNA foci

DNA polymerases of the Y-family are involved in translesion DNA synthesis past different types of DNA damage. Previous work has shown that DNA polymerases eta and iota are localised in replication factories during S phase, where they colocalise one-to-one with PCNA. Cells with factories containing these polymerases accumulate after treatment with DNA damaging agents because replication forks are stalled at sites of damage. We now show that DNA polymerase kappa (polkappa) has a different localisation pattern. Although, like the other Y-family polymerases, it is exclusively localised in the nucleus, polkappa is found in replication foci in only a small proportion of S-phase cells. It does not colocalise in those foci with proliferating cell nuclear antigen (PCNA) in the majority of cells. This reduced number of cells with polkappa foci, when compared with those containing poleta foci, is observed both in untreated cells and in cells treated with hydroxyurea, UV irradiation or benzo[a]pyrene. The C-terminal 97 amino acids of polkappa are sufficient for this limited localisation into nuclear foci, and include a C2HC zinc finger, bipartite nuclear localisation signal and putative PCNA binding site.