MEC1-DEPENDENT PHOSPHORYLATION OF RAD9P IN RESPONSE TO DNA-DAMAGE

In budding yeast, DNA damage can activate a checkpoint surveillance sy stem controlled by the RADS, RAD53, and MEC1 genes, resulting in a del ay in cell cycle progression. Here, I report that DNA damage induces r apid and extensive phosphorylation of Rad9p in a manner that correlate s directly with checkpoint activation. This response is dependent on M EC1, which encodes a member of the evolutionarily conserved ATM family of protein kinases, and on gene products of the RAD24 epistasis group , which have been implicated in the recognition and processing of DNA lesions. Since the phosphorylated form of Rad9p appears capable of int eracting stably with Rad53p in vivo, this phosphorylation response lik ely controls checkpoint signaling by Rad9p.