We have determined the nucleotide sequence of a 3.3 kb fragment containing the gene (ADE2) encoding phosphoribosylaminoimidazole carboxylase (AIRC) from the yeast Schwanniomyces occidentalis. Translation of a 1671 bp open reading frame predicts a protein of 557 amino acids which has significant homology to AIRC from Saccharomyces cerevisiae and Schizosaccharomyces pombe. The 5' untranslated region of the S. occidentalis gene contains a sequence corresponding to the consensus binding site of the S. cerevisiae transcription regulatory proteins GCN4, BAS1 and BAS2.