ASSEMBLY OF A CHROMOSOMAL REPLICATION MACHINE - 2 DNA-POLYMERASES, A CLAMP LOADER, AND SLIDING CLAMPS IN ONE HOLOENZYME PARTICLE .1. ORGANIZATION OF THE CLAMPS LOADER

The gamma complex of DNA polymerase III holoenzyme, the replicase of E scherichia coli, couples ATP hydrolysis to the loading of beta sliding clamps onto primed DNA. The beta sliding clamp tethers the holoenzyme replicase to DNA for rapid and processive synthesis. In this report, the gamma complex has been constituted hom its five different subunits . Size measurements and subunit stoichiometry studies show a compositi on of gamma(2) delta(1) delta'(1) chi(1) psi(1). Strong intersubunit c ontacts have been identified by gel filtration, and weaker contacts we re identified by surface plasmon resonance measurements. An analogous tau complex has also been constituted and characterized; it is nearly as active as the gamma complex in clamp loading activity, but as shown in the fourth report of this series, it is at a disadvantage in bindi ng the delta, delta', chi, and psi subunits when core is present (Xiao , Il., Naktinis, V., and O'Donnell, M. (1995) J. Biol. Chem. 270, 1337 8-13383). The single copy subunits within the gamma complex provide th e basis for the structural asymmetry inherent within DNA polymerase II I holoenzyme.