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

摘要

In response to genotoxic stress, a transient arrest in cell-cycle progression enforced by the DNA-damage checkpoint (DDC) signalling pathway positively contributes to genome maintenance. Because hyperactivated DDC signalling can lead to a persistent and detrimental cell-cycle arrest, ceDs must tightly regulate the activity of the kinases involved in this pathway. Despite their importance, the mechanisms for monitoring and modulating DDC signalling are not fully understood. Here we show that the DNA-repair scaffolding proteins Slx4 and Rtt107 prevent the aberrant hyperactivation of DDC signalling by lesions that are generated during DNA replication in Saccharomyces cerevisiae. On replication stress, cells lacking Slx4 or Rtt107 show hyperactivation of the downstream DDC kinase Rad53, whereas activation of the upstream DDC kinase Mecl remains normal. An Slx4-Rtt107 complex counteracts the checkpoint adaptor Rad9 by physically interacting with Dpbll and phosphorylated histone H2A, two positive regulators of Rad9-dependent Rad53 activation. A decrease in DDC signalling results from hypomorphic mutations in RAD53 and H2A and rescues the hypersensitivity to replication stress of cells lacking Slx4 or Rtt107. We propose that the Slx4-Rtt107 complex modulates Rad53 activation by a competition-based mechanism that balances the engagement of Rad9 at replication-induced lesions. Our findings show that DDC signalling is monitored and modulated through the direct action of DNA-repair factors.%DNA损伤或复制压力诱导检查点激酶的激发，rn该激酶使细胞周期暂停，以便DNA修复能够rn进行。然而，检查点激发必须予以调控，以rn防止细胞周期停滞在损伤被修复后持久存在。rnMarcus Smolka及其同事已经确定，由DNA修rn复支架蛋白Slx4和Rtt107形成的一种复合物与rnDpb11和磷酸化的组蛋白H2A(它们是激发rnRad53激酶的“检查点适配器”Rad9的正调控rn因子)发生相互作用。这样，Slx4-Rtt107复合rn物便通过直接监测DNA损伤(由Dpb11结合及rnH2A磷酸化来衡量)来调控检查点激酶的活性。