Saccharomyces cerevisiae Σ1278b Has Novel Genes of the N-Acetyltransferase Gene Superfamily Required for l-Proline Analogue Resistance

We discovered on the chromosome of Saccharomyces cerevisiae Σ1278b novel genes involved in l-proline analogue l-azetidine-2-carboxylic acid resistance which are not present in the standard laboratory strains. The 5.4 kb-DNA fragment was cloned from the genomic library of the l-azetidine-2-carboxylic acid-resistant mutant derived from a cross between S. cerevisiae strains S288C and Σ1278b. The nucleotide sequence of a 4.5-kb segment exhibited no identity with the sequence in the genome project involving strain S288C. Deletion analysis indicated that one open reading frame encoding a predicted protein of 229 amino acids is indispensable for l-azetidine-2-carboxylic acid resistance. The protein sequence was found to be a member of the N-acetyltransferase superfamily. Genomic Southern analysis and gene disruption showed that two copies of the novel gene with one amino acid change at position 85 required for l-azetidine-2-carboxylic acid resistance were present on chromosomes X and XIV of Σ1278b background strains. When this novel MPR1 or MPR2 gene (sigma 1278b gene for l-proline analogue resistance) was introduced into the other S. cerevisiae strains, all of the recombinants were resistant to l-azetidine-2-carboxylic acid, indicating that both MPR1 and MPR2 are expressed and have a global function in S. cerevisiae.