Post-replicative base excision repair in replication foci

Base excision repair (BER) is initiated by a DNA glycosylase and is complet ed by alternative routes, one of which requires proliferating cell nuclear antigen (PCNA) and other proteins also involved in DNA replication, We repo rt that the major nuclear uracil-DNA glycosylase (UNG2) increases in S phas e, during which it co-localizes with incorporated BrdUrd in replication foc i. Uracil is rapidly removed from replicatively incorporated dUMP residues in isolated nuclei. Neutralizing antibodies to UNG2 inhibit this removal, i ndicating that UNG2 is the major uracil-DNA glycosylase responsible. PCNA a nd replication protein A (RPA) co-localize with UNG2 in replication foci, a nd a direct molecular interaction of UNG2 with PCNA (one binding site) and PPA (two binding sites) was demonstrated using two-hybrid assays, a peptide SPOT assay and enzyme-linked immunosorbent assays. These results demonstra te rapid post-replicative removal of incorporated uracil by UNG2 and indica te the formation of a BER complex that contains UNG2, RPA and PCNA close to the replication fork.