Inactivating pentapeptide insertions in the fission yeast replication factor C subunit Rfc2 cluster near the ATP-binding site and arginine finger motif

Replication factor C (RFC) plays a key role in eukaryotic chromosome replication by acting as a loading factor for the essential sliding clamp and polymerase processivity factor, proliferating cell nuclear antigen (PCNA). RFC is a pentamer comprising a large subunit, Rfc1, and four small subunits, Rfc2-Rfc5. Each RFC subunit is a member of the AAA(+) family of ATPase and ATPase-like proteins, and the loading of PCNA onto double-stranded DNA is an ATP-dependent process. Here, we describe the properties of a collection of 38 mutant forms of the Rfc2 protein generated by pentapeptide-scanning mutagenesis of the fission yeast rfc2 gene. Each insertion was tested for its ability to support growth in fission yeast rfc2 delta cells lacking endogenous Rfc2 protein and the location of each insertion was mapped onto the 3D structure of budding yeast Rfc2. This analysis revealed that the majority of the inactivating mutations mapped in or adjacent to ATP sites C and D in Rfc2 (arginine finger and P-loop, respectively) or to the five-stranded beta sheet at the heart of the Rfc2 protein. By contrast, nonlethal mutations map predominantly to loop regions or to the outer surface of the RFC complex, often in highly conserved regions of the protein. Possible explanations for the effects of the various insertions are discussed.