The yeast AAP1 gene, encoding a putative amino-peptidase, was isolated based on its ability to suppress the temperature-sensitive growth on nonfermentable carbon sources of spr5, a stationary phase regulatory mutant. AAP1 was physically mapped to chromosome VIII between PUT2 and CUP1. Sequence analysis of the AAP1 gene showed a 1581-nucleotide open reading frame capable of encoding a 59-kilodalton protein. The protein encoded by this open reading frame exhibits approximately 40% sequence identity to human, rat, and mouse aminopeptidases. In limited regions, sequence identity between Aap1 and the mammalian aminopeptidases ranges from 53% to 93%. Insertional inactivation of the AAP1 gene resulted in a decrease in glycogen accumulation and the loss of the major band of arginine/alanine aminopeptidase activity. Strains carrying the AAP1 gene on a high copy plasmid show an increase in the major arginine/alanine aminopeptidase activity, a dramatic increase in glycogen accumulation, and an increase in transcription from a vector carrying lacZ fused to the promoter of a gene (SSA3) expressed during post-diauxic and stationary phases of the culture cycle. We conclude that although the AAP1 gene is not essential for viability, the Aap1 protein positively affects glycogen accumulation in yeast.