Ccr4-Not Complex mRNA Deadenylase Activity Contributes to DNA Damage Responses in Saccharomyces cerevisiae

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Abstract
DNA damage checkpoints regulate gene expression at the transcriptional and post-transcriptional level. Some components of the yeast Ccr4-Not complex, which regulates transcription as well as transcript turnover, have previously been linked to DNA damage responses, but it is unclear if this involves transcriptional or post-transcriptional functions. Here we show that CCR4 and CAF1, which together encode the major cytoplasmic mRNA deadenylase complex, have complex genetic interactions with the checkpoint genes DUN1, MRC1, RAD9, and RAD17 in response to DNA-damaging agents hydroxyurea (HU) and methylmethane sulfonate (MMS). The exonuclease-inactivating ccr4-1 point mutation mimics ccr4Δ phenotypes, including synthetic HU hypersensitivity with dun1Δ, demonstrating that Ccr4-Not mRNA deadenylase activity is required for DNA damage responses. However, ccr4Δ and caf1Δ DNA damage phenotypes and genetic interactions with checkpoint genes are not identical, and deletions of some Not components that are believed to predominantly function at the transcriptional level rather than mRNA turnover, e.g., not5Δ, also lead to increased DNA damage sensitivity and synthetic HU hypersensitivity with dun1Δ. Taken together, our data thus suggest that both transcriptional and post-transcriptional functions of the Ccr4-Not complex contribute to the DNA damage response affecting gene expression in a complex manner.