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
Nat Struct Mol Biol
Date: Apr. 01, 2022
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