An FHA domain–mediated protein interaction network of Rad53 reveals its role in polarized cell growth

The DNA damage checkpoint kinase Rad53 is important for the survival of budding yeast under genotoxic stresses. We performed a biochemical screen to identify proteins with specific affinity for the two Forkhead associated (FHA) domains of Rad53. The N-terminal FHA1 domain was found to coordinate a complex protein interaction network, which includes nuclear proteins involved in DNA damage checkpoints and transcriptional regulation. Unexpectedly, cytosolic proteins involved in cytokinesis, including septins, were also found as FHA1 binding proteins. Consistent with this interaction, a Rad53 mutant defective in its nuclear localization was found to localize to the bud neck. Abnormal morphology was observed in cells overexpressing the FHA1 domain and in rad53Δ cells under DNA replication stress. Further, septin Shs1 appears to have an important role in the response to DNA replication stress. Collectively, the results suggest a novel function of Rad53 in the regulation of polarized cell growth in response to DNA replication stress.