The evolutionarily conserved zinc finger motif in the largest subunit of human replication protein A is required for DNA replication and mismatch repair but not for nucleotide excision repair

The largest subunit of the replication protein (RPA) contains an evolutionarily conserved zinc finger motif that lies outside of the domains required for binding to single-stranded DNA or forming the RPA holocomplex. In previous studies, we showed that a point mutation in this motif (RPA^m) cannot support SV40 DNA replication. We have now investigated the role of this motif in several steps of DNA replication and in two DNA repair pathways. RPA^m associates with T antigen, assists the unwinding of double- stranded DNA at an origin of replication, stimulates DNA polymerases α and δ, and supports the formation of the initial short Okazaki fragments. However, the synthesis of a leading strand and later Okazaki fragments is impaired. In contrast, RPA^m can function well during the incision step of nucleotide excision repair and in a full repair synthesis reaction, with either UV-damaged or cisplatin-adducted DNA. Two deletion mutants of the Rpa1 subunit (eliminating amino acids 1-278 or 222-411) were not functional in nucleotide excision repair. We report for the first time that wild type RPA is required for a mismatch repair reaction in vitro. Neither the deletion mutants nor RPA^m can support this reaction. Therefore, the zinc finger of the largest subunit of RPA is required for a function that is essential for DNA replication and mismatch repair but not for nucleotide excision repair.