The regulatory gene PDC2 was identified in a screen for mutations affecting pyruvate decarboxylase activity in yeast. I have cloned and sequenced this gene. The predicted protein of 925 amino acids has no homology to any sequence in the databases. However, the protein sequence is rich in asparagine and serine residues, as is often found for transcriptional regulators. The PDC2 deletion mutant exhibits a phenotype very similar to, but more severe than that of the point mutant: a strongly reduced pyruvate decarboxylase specific activity, slow, respiration-dependent growth on glucose, and accumulation of pyruvate. The activity of other glycolytic enzymes seems to be unaffected by the pdc2 delta mutation. Synthesis of pyruvate decarboxylase is regulated by PDC2 at the transcriptional level. Expression of the major structural gene for pyruvate decarboxylase, PDC1, is strongly reduced in pdc2 delta mutants. Transcription of the generally more weakly expressed PDC5 gene appears to be entirely abolished. However, glucose induction of pyruvate decarboxylase synthesis is unaffected. Thus, PDC2 is either important for a high basal level of PDC gene expression or it plays a positive role in the autoregulation that controls expression of PDC1 and PDC5.