We cloned and sequenced the pyruvate decarboxylase (PDC; EC 4.1.1.1) structural gene KIPDCA in the yeast Kluyveromyces lactis and found it to be allelic to the previously isolated rag6 mutation. The putative amino acid sequence of the KIPdcAp appeared to be highly homologous to those of the yeast Pdc proteins identified so far. The disruption of KIPDCA indicated that it is the only PDC structural gene in K. lactis, as evidenced by the lack of PDC activity and ethanol production in the pdcA delta strains and by the absence of growth on glucose in the presence of respiratory inhibitors. It was observed that expression of the KIPDCA gene is induced by glucose at the transcriptional level. Transcription of the gene was reduced in the rag1, rag2, rag5 and rag8 mutants, which are defective for the low-affinity glucose permease, phosphoglucose isomerase, hexokinase, and a positive regulator of RAG1 expression, respectively.