ATR

ATR (ATM- and Rad3-related) is a serine/threonine kinase activated by replication stress - stalled replication forks and the single-stranded DNA exposed during repair.

Function

ATR is recruited by its partner ATRIP to single-stranded DNA coated with RPA, the structure that appears whenever a replication fork stalls or a resected break is awaiting repair. Activated ATR phosphorylates CHK1, which then enforces the intra-S and G2/M checkpoints, stabilizes stalled forks, suppresses origin firing elsewhere in the genome, and coordinates repair. The ATR-CHK1 arm therefore protects cells through S and G2, the phases in which unreplicated or partially replicated DNA would otherwise be segregated into