Structure of the DNA Damage-inducible Gene DDR48 and Evidence for Its Role in Mutagenesis in Saccharomyces Cerevisiae

The DDR48 gene of Saccharomyces cerevisiae is a member of a set of genes that displays increased transcription in response to treatments that produce DNA lesions or to heat-shock stress. Other members of this group include the DDRA2 and UBI4 genes. DNA sequence analysis of the DDR48 gene demonstrates the presence of two overlapping open reading frames, each of which has the capacity to encode a protein with a molecular mass of approximately 45 kilodaltons. Fusions of the DDR48 coding sequences to lacZ demonstrates that only one of these frames is expressed in yeast cells. The protein predicted from this sequence is extremely hydrophilic and contains multiple repeats of the peptide sequence Ser-Asn-Asn-X-Asp-Ser-Tyr-Gly where X is either Asn or Asp. Additionally, closely related sequences are found throughout the primary sequence. Primer extension data indicate that, after 4-nitroquinoline-1-oxide and heat-shock treatments, there are three major and two minor transcriptional start sites which are utilized. The function of the DDR48 gene was investigated by disrupting this gene in diploid cells. Viable haploid cells containing the DDR48 gene disruption were isolated after tetrad analysis. Although the ddr48 mutant showed a slightly altered sensitivity to killing by 4-nitroquinoline-1-oxide and to heat shock compared with the DDR48 haploid, the spontaneous mutation rate of reversion of a his4 mutation was reduced 6- to 14-fold in the ddr48 strain. These results implicate the DDR48 gene in the production or recovery of mutations in S. cerevisiae.