Distinct associations of the Saccharomyces cerevisiae Rad9 protein link Mac1-regulated transcription to DNA repair.

While it is known that ScRad9 DNA damage checkpoint protein is recruited to damaged DNA by recognizing specific histone modifications, here we report a different way of Rad9 recruitment on chromatin under non DNA damaging conditions. We found Rad9 to bind directly with the copper-modulated transcriptional activator Mac1, suppressing both its DNA binding and transactivation functions. Rad9 was recruited to active Mac1-target promoters (CTR1, FRE1) and along CTR1 coding region following the association pattern of RNA polymerase (Pol) II. Hir1 histone chaperone also interacted directly with Rad9 and was partly required for its localization throughout CTR1 gene. Moreover, Mac1-dependent transcriptional initiation was necessary and sufficient for Rad9 recruitment to the heterologous ACT1 coding region. In addition to Rad9, Rad53 kinase also localized to CTR1 coding region in a Rad9-dependent manner. Our data provide an example of a yeast DNA-binding transcriptional activator that interacts directly with a DNA damage checkpoint protein in vivo and is functionally restrained by this protein, suggesting a new role for Rad9 in connecting factors of the transcription machinery with the DNA repair pathway under unchallenged conditions.

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