DNA POLYMERASE-III ACCESSORY PROTEINS .4. CHARACTERIZATION OF CHI ANDPSI

The gamma complex (gammadeltadelta'chipsi) subassembly of the Escheric hia coli replicase initiates processive replication upon assembling th e ring-shaped beta subunit around DNA. The beta ring acts as a clamp t o hold the replicase down to DNA for highly processive synthesis. In t his report we characterize the chi and psi subunits of the gamma compl ex. Both chi and psi are monomeric, and they associate to form a 1:1 c omplex. The chi subunit does not form a complex with gamma, but psi bi nds gamma tightly thereby acting as a bridge to assimilate chi into th e gamma complex structure. The psi subunit stimulated the ATPase and r eplication activities of gamma. The chi subunit only stimulated the ac tivities of gamma when the psi subunit was also present thus reflectin g the structure where psi bridges the interaction of chi with gamma.