Mechanisms of loading and release of the 9-1-1 checkpoint clamp.

Juan C Castaneda, Marina Schrecker, Dirk Remus, Richard K Hite

Nature structural & molecular biology 2022 Apr

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Single-stranded or double-stranded DNA junctions with recessed 5' ends serve as loading sites for the checkpoint clamp, 9-1-1, which mediates activation of the apical checkpoint kinase, ATRMec1. However, the basis for 9-1-1's recruitment to 5' junctions is unclear. Here, we present structures of the yeast checkpoint clamp loader, Rad24-replication factor C (RFC), in complex with 9-1-1 and a 5' junction and in a post-ATP-hydrolysis state. Unexpectedly, 9-1-1 adopts both closed and planar open states in the presence of Rad24-RFC and DNA. Moreover, Rad24-RFC associates with the DNA junction in the opposite orientation of processivity clamp loaders with Rad24 exclusively coordinating the double-stranded region. ATP hydrolysis stimulates conformational changes in Rad24-RFC, leading to disengagement of DNA-loaded 9-1-1. Together, these structures explain 9-1-1's recruitment to 5' junctions and reveal new principles of sliding clamp loading. © 2022. The Author(s), under exclusive licence to Springer Nature America, Inc.

Citation

Juan C Castaneda, Marina Schrecker, Dirk Remus, Richard K Hite. Mechanisms of loading and release of the 9-1-1 checkpoint clamp. Nature structural & molecular biology. 2022 Apr;29(4):369-375