External and internal DNA-damaging agents continually threaten the integrity of genetic material in cells. Although a;variety of repair mechanisms exist to remove the resulting lesions, some lesions escape repair and block the;replication machinery. Members of the Y family of DNA polymerases, such as POLK, permit the continuity of the;replication fork by allowing replication through such DNA lesions. Each Y family polymerase has a unique DNA-damage;bypass and fidelity profile. POLK is specialized for the extension step of lesion bypass (summary by Lone et al., 2007;(PubMed 17317631)).