Kinetic Analysis of Arginine-Finger Motif Function in S. cerevisiae Clamp Loader

Replication factor C (RFC) loads a circular clamp, proliferating cell nuclear antigen (PCNA), onto a primer-template junction at the replication fork during DNA replication. RFC consists of five subunits, A-E, each of which belongs to the AAA+ family member of ATPases. The subunits are arranged in an open ring form with four ATPase sites located at the interfaces of subunits A-B, B-C, C-D and D-E. In each ATPase site, an Arginine-finger motif (SRC), which is provided by the adjacent subunit, is implicated in sensing ATP binding and regulating ATP hydrolysis. According to a recent study of SRC→SAC point mutations, it appears that RFC subunits play distinct roles during clamp assembly (Johnson, et al. 2006). We analyzed these mutants by measuring their pre-steady state functions of DNA binding and ATPase activities. We found that CSAC (Binactive) and DSAC (Cinactive) mutants have severe defects in DNA binding, while BSAC (Ainactive) and ESAC (Dinactive) mutants have severe defects in DNA dissociation. These disruptions in RFC interactions with DNA, and corresponding effects of RFC ATPase activities, elucidate further the distinct functions of individual RFC subunits in the clamp assembly reaction.Reference: Johnson A. et al., (2006) J. Biol. Chem. 281, 35531-35543.