7sgz
From Proteopedia
Structure of the yeast Rad24-RFC loader bound to DNA and the closed 9-1-1 clamp
Structural highlights
FunctionRAD24_YEAST Participates in checkpoint pathways arrest of the cell cycle, a mechanism that allows the DNA repair pathways to act to restore the integrity of the DNA prior to DNA synthesis or separation of the replicated chromosomes. Regulates the DNA damage checkpoint pathway throughout the cell cycle, when associated with RCF5. Component of the RFC-like RAD24-RFC complex which loads the checkpoint clamp DDC1:MEC3:RAD17 complex and is involved in DNA repair pathways. During a clamp loading circle, the RFC:clamp complex binds to DNA and the recognition of the double-stranded/single-stranded junction stimulates ATP hydrolysis by RFC. The complex presumably provides bipartite ATP sites in which one subunit supplies a catalytic site for hydrolysis of ATP bound to the neighboring subunit. Dissociation of RFC from the clamp leaves the clamp encircling DNA.[1] [2] [3] Publication Abstract from PubMedThe 9-1-1 DNA checkpoint clamp is loaded onto 5'-recessed DNA to activate the DNA damage checkpoint that arrests the cell cycle. The 9-1-1 clamp is a heterotrimeric ring that is loaded in Saccharomyces cerevisiae by Rad24-RFC (hRAD17-RFC), an alternate clamp loader in which Rad24 replaces Rfc1 in the RFC1-5 clamp loader of proliferating cell nuclear antigen (PCNA). The 9-1-1 clamp loading mechanism has been a mystery, because, unlike RFC, which loads PCNA onto a 3'-recessed junction, Rad24-RFC loads the 9-1-1 ring onto a 5'-recessed DNA junction. Here we report two cryo-EM structures of Rad24-RFC-DNA with a closed or 27-A open 9-1-1 clamp. The structures reveal a completely unexpected mechanism by which a clamp can be loaded onto DNA. Unlike RFC, which encircles DNA, Rad24 binds 5'-DNA on its surface, not inside the loader, and threads the 3' ssDNA overhang into the 9-1-1 clamp from above the ring. DNA is loaded through the 9-1-1 DNA checkpoint clamp in the opposite direction of the PCNA clamp.,Zheng F, Georgescu RE, Yao NY, O'Donnell ME, Li H Nat Struct Mol Biol. 2022 Apr;29(4):376-385. doi: 10.1038/s41594-022-00742-6. , Epub 2022 Mar 21. PMID:35314830[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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