Abstract
Endogenous DNA lesions are produced through the misincorporation of damaged nucleotides during DNA replication, in addition to direct acting of endogenous mutagens to DNA. Oxidation and deamination are the most established endogenous sources for nucleotide lesions. Thus to know the sanitizing mechanisms for the endogenous nucleotide lesions is important for understanding the mechanism of spontaneous mutagenesis and genomic instability.
For this purpose we first isolated the sanitizing enzymes in Saccharomyces cerevisiae for oxidized nucleotide lesions, Ylr151c, and for deaminated nucleotide lesions, Ham1, and characterized them as pyrophosphatases for these nucleotide lesions. We next constructed the strains deficient in either YLR151c or HAM1 in both haploid and diploid cells, and examined spontaneous frequency of mutation in haploid cells and of loss of heterozygosity (LOH) in diploid cells. In haploid cells, the deficiency in YLR151c caused mild mutator phenotype, while that of HAM1 did not show any effects on spontaneous mutagenesis. However, in diploid cells, the deficiency in HAM1 caused 20-fold induction of LOH through hyper-induction of homologous recombination. These results indicate that endogenous nucleotide lesions cause not only mutagenesis in haploid cells but also genomic instability through hyper-recombination and LOH in diploid cells.
Referense; Nucleic Acids Res. 32, 5339-5348 (2004), Biochem. Biophys. Res. Commun. 325, 928-933 (2004)
