Identification of the critical region in replication factor C from Pyrococcus furiosus for the stable complex formation with proliferating cell nuclear antigen and DNA.

Replication factor C (RFC) and proliferating cell nuclear antigen (PCNA) are accessory proteins essential for processive DNA synthesis. The function of RFC is to load PCNA, a processivity factor of replicative DNA polymerases, onto primed DNA templates. The central hole of the PCNA homo-trimeric ring encircles doublestranded DNA, so that DNA polymerases can operate for DNA synthesis with PCNA along a DNA template. The Pyrococcus furiosus RFC (PfuRFC) consists of a small subunit (RFCS, 37kDa) and a large subunit (RFCL, 55kDa), which show significant sequence identity to the eukaryotic homologs. The C-terminal region of RFCL has an acidic cluster of about 30 amino acids, which consists mainly of glutamic acid residues, and a following basic cluster of 10 amino acids, which consists mainly of lysine residues. These clusters of charged amino acids, which precede the C-terminal consensus sequence, PIP (PCNA interacting protein)-box, are conserved in several archaeal RFCLs. The series of mutant PfuRFC containing the C-terminal deletions in RFCL were constructed. The mutational analyses showed that the charged cluster is not essential for loading of PCNA onto DNA. However, the region containing the basic cluster is important for the stable ternary (RFC-PCNA-DNA) complex formation.