title: Cyclin-dependent kinase inhibitor p21 modulates the DNA primer-template recognition complex.
abstract: The p21 protein, a cyclin-dependent kinase (CDK) inhibitor, is capable of binding to both cyclin-CDK and the proliferating cell nuclear antigen (PCNA). Through its binding to PCNA, p21 can regulate the function of PCNA differentially in replication and repair. To gain an understanding of the precise mechanism by which p21 affects PCNA function, we have designed a new assay for replication factor C (RFC)-catalyzed loading of PCNA onto DNA, a method that utilizes a primer-template DNA attached to agarose beads via biotin-streptavidin. Using this assay, we showed that RFC remains transiently associated with PCNA on the DNA after the loading reaction. Addition of p21 did not inhibit RFC-dependent PCNA loading; rather, p21 formed a stable complex with PCNA on the DNA. In contrast, the formation of a p21-PCNA complex on the DNA resulted in the displacement of RFC from the DNA. The nonhydrolyzable analogs of ATP, adenosine-5'-O-(3-thiotriphosphate) (ATPgammaS) and adenyl-imidodiphosphate, each stabilized the primer recognition complex containing RFC and PCNA in the absence of p21. RFC in the ATPgammaS-activated complex was no longer displaced from the DNA by p21. We propose that p21 stimulates the dissociation of the RFC from the PCNA-DNA complex in a process that requires ATP hydrolysis and then inhibits subsequent PCNA-dependent events in DNA replication. The data suggest that the conformation of RFC in the primer recognition complex might change on hydrolysis of ATP. We also suggest that the p21-PCNA complex that remains attached to DNA might function to tether cyclin-CDK complexes to specific regions of the genome.
authors.affiliation: Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA.
authors.forename: S
authors.initials: S
authors.lastname: Waga
authors.forename: B
authors.initials: B
authors.lastname: Stillman
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000266:Adenylyl Imidodiphosphate / Q000494:pharmacology; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism*; D017931:DNA Primers; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000378:metabolism*; D018398:Homeodomain Proteins; D006801:Humans; D015778:Minor Histocompatibility Antigens; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D051716:Replication Protein A; D051818:Replication Protein C; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D013698:Templates, Genetic
chemical_list: C096816:BCL2-related protein A1; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D017931:DNA Primers; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D018398:Homeodomain Proteins; C096063:MATA1 protein, S cerevisiae; D015778:Minor Histocompatibility Antigens; D018809:Proliferating Cell Nuclear Antigen; D019253:Proto-Oncogene Proteins c-bcl-2; C497167:RPA1 protein, human; D011993:Recombinant Fusion Proteins; D051716:Replication Protein A; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D000266:Adenylyl Imidodiphosphate; C022571:adenosine 5'-O-(3-thiotriphosphate); D000255:Adenosine Triphosphate; D051818:Replication Protein C