Assembly of a Chromosomal Replication Machine: Two DNA Polymerases, a Clamp Loader, and Sliding Clamps in One Holoenzyme Particle. I. ORGANIZATION OF THE CLAMP LOADER

• Published in: The Journal of biological chemistry 1995-06, Vol.270 (22), p.13348-13357
• Main Authors: Onrust, Rene, Finkelstein, Jeff, Naktinis, Vytautas, Turner, Jennifer, Fang, Linhua, O'Donnell, Mike
• Format: Article
• Language: English
• Subjects: Chromatography, High Pressure Liquid; Chromosomes, Bacterial; DNA Polymerase III - metabolism; DNA Replication; DNA, Bacterial - metabolism; Electrophoresis, Polyacrylamide Gel; Escherichia coli; Escherichia coli - enzymology; Escherichia coli - genetics
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.270.22.13348

The γ complex of DNA polymerase III holoenzyme, the replicase of Escherichia coli, couples ATP hydrolysis to the loading of β sliding clamps onto primed DNA. The β sliding clamp tethers the holoenzyme replicase to DNA for rapid and processive synthesis. In this report, the γ complex has been constituted from its five different subunits. Size measurements and subunit stoichiometry studies show a composition of γ2δ1δ′1χ1ψ1. Strong intersubunit contacts have been identified by gel filtration, and weaker contacts were identified by surface plasmon resonance measurements. An analogous τ complex has also been constituted and characterized; it is nearly as active as the γ complex in clamp loading activity, but as shown in the fourth report of this series, it is at a disadvantage in binding the δ, δ′, χ, and ψ subunits when core is present (Xiao, H., Naktinis, V., and O'Donnell, M. (1995) J. Biol. Chem. 270, 13378-13383). The single copy sub-units within the γ complex provide the basis for the structural asymmetry inherent within DNA polymerase III holoenzyme.