title: Interplay of clamp loader subunits in opening the beta sliding clamp of Escherichia coli DNA polymerase III holoenzyme.
abstract: The Escherichia coli beta dimer is a ring-shaped protein that encircles DNA and acts as a sliding clamp to tether the replicase, DNA polymerase III holoenzyme, to DNA. The gamma complex (gammadeltadelta'chipsi) clamp loader couples ATP to the opening and closing of beta in assembly of the ring onto DNA. These proteins are functionally and structurally conserved in all cells. The eukaryotic equivalents are the replication factor C (RFC) clamp loader and the proliferating cell nuclear antigen (PCNA) clamp. The delta subunit of the E. coli gamma complex clamp loader is known to bind beta and open it by parting one of the dimer interfaces. This study demonstrates that other subunits of gamma complex also bind beta, although weaker than delta. The gamma subunit like delta, affects the opening of beta, but with a lower efficiency than delta. The delta' subunit regulates both gamma and delta ring opening activities in a fashion that is modulated by ATP interaction with gamma. The implications of these actions for the workings of the E. coli clamp loading machinery and for eukaryotic RFC and PCNA are discussed.
authors.affiliation: Department of Pharmacology, Joan and Sanford I. Weill Graduate School of Medical Sciences of Cornell University, New York, NY 10021, USA.
authors.forename: F P
authors.initials: FP
authors.lastname: Leu
authors.forename: M
authors.initials: M
authors.lastname: O'Donnell
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D020816:Amino Acid Motifs; D002384:Catalysis; D018360:Crystallography, X-Ray; D004247:DNA / Q000378:metabolism; D004258:DNA Polymerase III / Q000737:chemistry*; D004268:DNA-Binding Proteins / Q000737:chemistry; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D004926:Escherichia coli / Q000201:enzymology*; D020035:Holoenzymes / Q000737:chemistry*; D008954:Models, Biological; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D051818:Replication Protein C; D020349:Surface Plasmon Resonance; D013997:Time Factors
chemical_list: D004268:DNA-Binding Proteins; D020035:Holoenzymes; D018809:Proliferating Cell Nuclear Antigen; D000255:Adenosine Triphosphate; D004247:DNA; D004258:DNA Polymerase III; D051818:Replication Protein C