A gene encoding a functional acetolactate synthase (ALS) subunit has been isolated from the fission yeast Schizosaccharomyces pombe, and has been structurally and genetically characterized. The approximate 5-kbp cloned DNA segment was found to contain a 2007-bp open reading frame capable of encoding a 669 aminoacid polypeptide which exhibited 57.1% similarity to the corresponding ALS subunit from Saccharomyces cerevisiae. The putative ilv1 isolated from S. pombe was shown to encode a functional subunit of acetolactate synthase by complementation of an S. cerevisiae strain deleted for the ILV2 locus.