Disruption of mouse SNM1 causes increased sensitivity to the DNA interstrand cross-linking agent mitomycin C

DNA interstrand cross-links (ICLs) represent lethal DNA damage, because the y block transcription, replication, and segregation of DNA. Because of thei r genotoxicity, agents inducing ICLs are often used in antitumor therapy. T he repair of ICLs is complex and involves proteins belonging to nucleotide excision, recombination, and translesion DNA repair pathways in Escherichia coli, Saccharomyces cerevisiae, and mammals. We cloned and analyzed mammal ian homologs of the S. cerevisiae gene SNM1 (PSO2), which is specifically i nvolved in ICL repair. Human Snm1, a nuclear protein, was ubiquitously expr essed at a very low level. We generated mouse SNM1(-/-) embryonic stem cell s and showed that these cells were sensitive to mitomycin C. In contrast to S. cerevisiae snm1 mutants, they were not significantly sensitive to other ICL agents, probably due to redundancy in mammalian ICL repair and the exi stence of other SNM1 homologs. The sensitivity to mitomycin C was complemen ted by transfection of the human SNM1 cDNA and by targeting of a genomic cD NA-murine SNM1 fusion construct to the disrupted locus. We also generated m ice deficient for murine SNM1. They were viable and fertile and showed no m ajor abnormalities. However, they were sensitive to mitomycin C. The ICL se nsitivity of the mammalian SNM1 mutant suggests that SNM1 function and, by implication, ICL repair are at least partially conserved between S. cerevis iae and mammals.