Suppression of the hydroxyurea-sensitivity of rad53 mutation by CYC8 in Saccharomyces cerevisiae

초록

Rad53 is an essential checkpoint kinase that plays a central role in cell cycle arrest at all checkpoints. It also functions in transcriptional activation in response to DNA damage. RNR, the key enzyme in the maintenance and regulation of dNTP biosynthesis, is one of the target genes for transcriptional control by Rad53. We previously found that a rad53 mutation renders yeast cells to be extremely sensitive to an RNR inhibitor, hydroxyurea. In this study, we screened multi-copy suppressor genes that suppress the hydroxyurea sensitivity of rad53 mutant, and identified CYC8 as a candidate gene. We found that either overexpression or deletion of CYC8 gene suppressed the hydroxyurea sensitivity of the mutant cells. In addition, deletion of Tub1, which forms a complex with Cyc8, also suppressed the HU sensitivity. Cyc8/Tup1 complex acts as a general transcriptional co-repressor. Consistence with this, the expression levels of RNR1 and RNR3 were elevated in cyc8Δ mutant cells. These results suggest that disturbance of Cyc8/Tup1 complex increase the level RNR enzyme, which, in turn, causes the rad53 mutant cells to be resistant to the treatment of hydroxyurea.