Abstract
Fifty-five isoleucine-valine requiring mutants were selected in a haploid strain of Saccharomyces cerevisiae after treatment with ethyl methanesulfonate. All the mutants could be assigned to the known complementation groups,ilv1 (threonine deaminase),ilv2 (acetohydroxyacid synthetase),ilv5 (acetohydroxyacid reductoisomerase) andilv3 (dihydroxyacid dehydrase). Intragenic complementation occurs in bothilv2 andilv5. The levels of α-acetohydroxyacids formed by these four types of mutants were consistent with the previous notion that the mutants define the structural genes coding for these enzymes. Chromosome assignment by the Rec (spo11) mapping method showed thatilv2 was located on chromosome XIII, andilv5 on chromosome XII. The locations were confirmed by mitotic analyses, using eitherrad52 homozygosis or benzimidazol carbamic acid methyl ester. Tetrad analysis placedilv2 on the right arm of chromosome XIII, 36 cM distal tolys7, andilv5 was positioned on the right arm of chromosome XII, distal to the ribosomal RNA gene cluster (rDNA) and proximal toura4.
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