DNA is loaded through the 9-1-1 DNA checkpoint clamp in the opposite direction of the PCNA clamp.
The 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.
Mesh Terms:
Cell Cycle Proteins, DNA, DNA Replication, Intracellular Signaling Peptides and Proteins, Proliferating Cell Nuclear Antigen, Replication Protein C, Saccharomyces cerevisiae, Saccharomyces cerevisiae Proteins
Cell Cycle Proteins, DNA, DNA Replication, Intracellular Signaling Peptides and Proteins, Proliferating Cell Nuclear Antigen, Replication Protein C, Saccharomyces cerevisiae, Saccharomyces cerevisiae Proteins
Nat Struct Mol Biol
Date: Apr. 01, 2022
PubMed ID: 35314830
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