Rph1, a Cys2-His2 zinc finger protein, binds to an upstream repressing sequence of the photolyase gene PHR1, and represses its transcription in response to DNA damage in Saccharomyces cerevisiae. In this report, we have demonstrated that the phosphorylation of Rph1 protein was increased in response to DNA damage. The DNA damage-induced phosphorylation of Rph1 was missing in most damage checkpoint mutants including rad9, rad17, mec1 and rad53. These results indicate that Rph1 phosphorylation is under the control of the Mec1-Rad53 damage checkpoint pathway. Rph1 phosphorylation required the kinase activity of Rad53 since it was significantly decreased in rad53 checkpoint mutant. Furthermore, loss of other kinases including Dun1, Tel1 and Chk1, which function downstream of Mec1, did not affect the Rph1 phosphorylation. This contrasts with the derepression of Crt1-regulated genes, which requires both Rad53 and Dun1 protein kinases. These results imply that post-translational modification of Rph1 repressor is regulated by a potentially novel damage checkpoint pathway that is distinct from the RAD53-DUN1-CRT1 cascade implicated in the DNA damage-dependent transcription of ribonucleotide reductase genes.
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