Single point mutation in ATR kinase FAT domain found to bypass DNA checkpoint activation requirements

Ataxia telangiectasia and Rad3-related (ATR) is a central kinase in the cellular response to replication stress and DNA damage. When replication forks stall or single-stranded DNA accumulates, ATR is activated to initiate cell cycle checkpoints that preserve genome integrity. The canonical activation model involves binding of an ATR-activating protein that relieves an autoinhibitory domain — the PIKK regulatory domain (PRD) — within the kinase. Upstream signalling through the 9-1-1 checkpoint clamp complex is generally considered necessary for full checkpoint activation.

Published in PLOS Genetics, a study by Kamal Dev and colleagues now reports that a single point mutation in the FAT domain of fission yeast Rad3ATR constitutively elevates kinase activity and renders the replication checkpoint independent of 9-1-1 complex phosphorylation. The FAT domain is a large structural region of PIKKs whose function in ATR regulation had been incompletely characterised.

The finding refines the mechanistic model of ATR activation, suggesting that the FAT domain plays a direct autoinhibitory role that is normally relieved by upstream signals, and that perturbation of this domain can uncouple checkpoint activation from its canonical requirements. The work has implications for understanding how ATR dysregulation may contribute to genome instability and for the design of ATR-targeting compounds in oncology research.

This is a peer-reviewed study in a model organism (Schizosaccharomyces pombe); translation to human ATR biology will require further investigation.