DNA-repair scaffolds dampen checkpoint signalling by counteracting the adaptor Rad9

Abstract

In response to genotoxic stress, a transient arrest in cell cycle progression enforced by the DNA damage checkpoint (DDC) signaling pathway positively contributes to genome maintenance1. Because hyperactivated DDC can lead to a persistent and detrimental cell cycle arrest2,3, cells must tightly regulate the activity of DDC kinases. Despite their importance, the mechanisms for monitoring and modulating DDC signaling are not fully understood. Here we show that DNA repair scaffolding proteins Slx4 and Rtt107 prevent lesions generated during DNA replication from aberrantly hyperactivating DDC signaling in Saccharomyces cerevisiae. Upon replication stress, cells lacking Slx4 or Rtt107 exhibit hyperactivation of the downstream DDC kinase Rad53 while activation of the upstream DDC kinase Mec1 remains normal. An Slx4-Rtt107 complex counteracts the checkpoint adaptor Rad9 by physically interacting with Dpb11 and phospho-H2A, two positive regulators of Rad9-dependent Rad53 activation. Reduction of DDC signaling by hypomorphic mutations in RAD53 and H2A rescue the hyper-sensitivity of slx4Δ or rtt107Δ cells to replication stress. We propose that the Slx4-Rtt107 complex modulates Rad53 activation via a competition-based mechanism that balances the engagement of Rad9 at replication-induced lesions. Our findings reveal that DDC signaling is monitored and modulated through the direct action of DNA repair factors.