Transcriptional regulation of DNA damage responsive (DDR) genes in different rad mutant strains of Saccharomyces cerevisiae

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Abstract
The roles of the RAD genes of Saccharomyces cerevisiae in the regulation of transcription of two DNA damage responsive (DDR) genes were investigated by examining the levels of the DDRA2 and DDR48 transcripts in different rad mutants after exposure to two different DNA damaging agents. Strains carrying mutations in either the RAD3, RAD6 or RAD52 genes were treated with increasing concentrations of 4-nitroquinoline-1-oxide (NQO) or N-methyl-N′-nitro-N-nitrosoguanidine (MNNG) and the DDR transcript levels were determined by Northern hybridization analysis. Our results indicate that the RAD3 gene is required for DDRA2 transcript production following NQO or MNNG treatments. Strains carrying mutations in either the RAD6 or RAD52 genes show an increased level of DDRA2 transcript in undamaged cells. However, the rad6 and rad52 mutants show a normal dose-dependent increase in DDRA2 transcript levels after NQO or MNNG exposure. The DDR48 gene appears to be regulated differently from DDRA2 in that this gene is induced in rad3 cells after damaging treatment but transcript induction is severely reduced in both rad6 and rad52 mutant strains. Although the rad mutations influence the kinetics of transcript accumulation, these effects do not account for the altered dose responses of the DDRA2 and DDR48 genes. Our results also demonstrate that the regulation of DDRA2 and DDR48 transcript levels by heat shock treatment is affected less severely in the different rad strains, a result which suggests that the RAD genes play an indirect role in DDR gene control. The different behavior of the DDRA2 and DDR48 genes in the various rad strains suggests that the regulatory responses of S. cerevisiae to DNA damage are complex.