THE PETITE-NEGATIVE YEAST KLUYVEROMYCES-LACTIS HAS A SINGLE-GENE EXPRESSING PYRUVATE DECARBOXYLASE ACTIVITY

We cloned and sequenced the pyruvate decarboxylase (PDC; EC 4.1.1.1) s tructural gene KIPDCA in the yeast Kluyveromyces lactis and found it t o be allelic to the previously isolated rag6 mutation. The putative am ino acid sequence of the KIPdcAp appeared to be highly homologous to t hose of the yeast Pdc proteins identified so far. The disruption of KI PDCA indicated that it is the only PDC structural gene in K. lactis, a s 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 pres ence of respiratory inhibitors. It was observed that expression of the KIPDCA gene is induced by glucose at the transcriptional level. Trans cription of the gene was reduced in the rag1, rag2, rag5 and rag8 muta nts, which are defective for the low-affinity glucose permease, phosph oglucose isomerase, hexokinase, and a positive regulator of RAG1 expre ssion, respectively.