The ADE1 gene of the yeast Pichia methanolica encodes phosphoribosyl-5-aminoimidazole-carboxylase (AIRC, EC 4.1.1.21), which is involved in purine biosynthesis. The gene was cloned by complementation of an ade2 mutation in Saccharomyces cerevisiae and a 3077 nucleotide DNA fragment was sequenced. The sequence possessed a single open reading frame, corresponding to a 543 amino acid sequence. The sequence of this putative protein has been compared to the proteins of homologous genes from S. cerevisiae, Schizosaccharomyces pombe, Escherichia coli, chicken and man. The analysis revealed remarkable homology between yeast AIRCs, while for other proteins homology was limited to defined regions.