Isolation and characterization of yeast mutants with thermoconditional sensitivity to the bifunctional alkylating agent nitrogen mustard

Abstract

Selection of mutants of Saccharomyces cerevisiae sensitive to the DNA cross-linking agent nitrogen mustard (HN2) at two temperatures (23 °C and 36 °C) yielded two isolates with thermoconditionally enhanced (ts) sensitivity to the mutagen. Both were due to single recessive nuclear genes. Mutant allele snm1-2 (ts) showed mainly ts-sensitivity to HN2, whereas mutant allele snm2-1 (ts) conferred ts-sensitivity to HN2, half mustard (HN1) and UV. In temperature-shift experiments it was determined that the functions of SNM1 and SNM2 are needed for recovery within 6 to 7 h. after mutagen exposure during incubation at 23 °C on YEPD when HN2 and UV are applied. After HN1 treatment the SNM2 coded function is required for recovery for about 14 hrs. This possibly indicates a handling of UV- and HN2-induced lesions different from that of HN1-induced lesions.

Role of PSO genes in repair of DNA damage of Saccharomyces cerevisiae

“…Temperature-shift experiments show a complete Pso2p function within 5-6 h after introduction of ICL by HN2 treatment [28]. Pso2p has a nuclear localisation signal and indeed is localized there [29].…”

“…Thermoconditional mutant snm1-2ts [28], now called pso2-12ts [7] carries two silent point and a missense mutation that replaces glycine with arginine at aa position 256 [29], thereby altering the hydrophilic domain of the protein. Temperature-shift experiments show a complete Pso2p function within 5-6 h after introduction of ICL by HN2 treatment [28].…”

Structure-specific endonuclease activity of SNM1A enables processing of a DNA interstrand crosslink

“…The importance of SNM1A in human ICL repair has only recently been appreciated ( 17 ), despite its yeast homologue (Pso2) having been shown to play an essential role in ICL repair ( 23 , 36 , 37 ). Prior studies demonstrating that SNM1A is able to rescue ICL repair defects in pso2 -deficient cells suggest that SNM1A and Pso2 share common activities required for ICL processing ( 22 ).…”

Sak1 kinase interacts with Pso2 nuclease in response to DNA damage induced by interstrand crosslink-inducing agents in Saccharomyces cerevisiae

“…Yeast mutants cells hypersensitive to ICL-inducing agents were identified in the early 1980s by two independent genetic screenings in Saccharomyces cerevisiae, which showed sensitivity to photoactivated psoralen (PSO2) [4] and sensitivity to nitrogen mustard (SNM1) [5]. It was later demonstrated that these genes are allelic [6] and the nomenclature PSO2 was adopted to unify them [1].…”