SNAP output for PDB entry 7sh2 [SNAP web server]

PDB-id

7sh2; SNAP-derived features in text and JSON formats; DNAproDB

Class

DNA binding protein-DNA

Method

cryo-EM (3.23 Å)

Summary

Structure of the yeast rad24-rfc loader bound to DNA and the open 9-1-1 clamp

Reference

Zheng F, Georgescu RE, Yao NY, O'Donnell ME, Li H (2022): "DNA is loaded through the 9-1-1 DNA checkpoint clamp in the opposite direction of the PCNA clamp." Nat.Struct.Mol.Biol., 29, 376-385. doi: 10.1038/s41594-022-00742-6.

Abstract

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-Å 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.