The set1 Delta mutation unveils a novel signaling pathway relayed by the Rad53-dependent hyperphosphorylation of replication protein A that leads to transcriptional activation of repair genes

SET domain proteins are present in chromosomal proteins involved in epigene tic control of transcription. The yeast SET domain protein Set1p regulates chromatin structure, DNA repair, and telomeric functions. We investigated t he mechanism by which the absence of Set1p increases DNA repair capacities of checkpoint mutants. We show that deletion of SETI induces a response rel ayed by the signaling kinase Rad53p that leads to the MEC1/TEL1-independent hyperphosphorylation of replication protein A middle subunit (Rfa2p). Cons equently, the binding of Rfa2p to upstream repressing sequences (URS) of re pair genes is decreased, thereby lending to their derepression. Our results correlate the set1 Delta -dependent phosphorylation of Rfa2p with the tran scriptional induction of repair genes. Moreover, we show that the deletion of the amino-terminal region of Rfa2p suppresses the sensitivity to ultravi olet radiation of a mec3 Delta checkpoint mutant, abolishes the URS-mediate d repression, and increases the expression of repair genes. This work provi des an additional link for the role of Rfa2p in the regulation of the repai r capacity of the cell and reveals a role for the phosphorylation of Rfa2p and unveils unsuspected connections between chromatin, signaling pathways, telomeres, and DNA repair.