Molecular cloning and genetic characterization of the Saccharomyces cerevisiae NGS1/MRE11 gene

The Saccharomyces cerevisiae ngs1-1 mutant alas previously identified by its enhanced sensitivity to simple DNA-alkylating agents such as methyl methanesulfonate but not to UV Molecular cloning and sequencing of NGS1 as a putative DNA-alkylation repair gene revealed that it is identical, to MRE11 a,gene that is involved in DNA recombinational repair. In order to investigate functional domains of the Mre11 protein, nucleotide-sequence alterations of a number of mre11 mutant alleles, including ngs1-1, mre11-1 (ts), mre11-2, mre11-3 and mre11-58, were determined. Most of these mutations map to the N-terminus of Mre11 It emphasizing the importance of this highly conserved domain. The ngs1-1 and mre11-3 mutants carry nonsense mutations resulting in truncated proteins. Missense mutations were found in mre11-1 (ts), mre11-2 and mre11-58, of which mre11-2 and mre11-58 mapped to the conserved phosphoesterase domains, indicating the involvement of these motifs in the: formation and/or processing of DNA double-strand breaks. Finally, mitotic-recombination! assays skew that the mrt lid mutation enhances inter-chromosomal recombination but decreases the intra-chromosomal deletion frequency. In addition. MRE11 appears to play different roles juring spontaneous and alkylation-induced homologous mitotic recombination.