RAG3 GENE AND TRANSCRIPTIONAL REGULATION OF THE PYRUVATE DECARBOXYLASE GENE IN KLUYVEROMYCES-LACTIS

The RAG3 gene has been cloned from a Kluyveromyces lactis genomic libr ary by complementation of the rag3 mutation, which shows impaired ferm entative growth on glucose in the presence of respiratory inhibitors. From the nucleotide sequence of the cloned DNA, which contained an ope n reading frame of 765 codons, the predicted protein is 49.5% identica l to the Pdc2 protein of Saccharomyces cerevisiae, a regulator of pyru vate decarboxylase in this yeast. Measurement of the pyruvate decarbox ylase activity in the original rag3-1 mutant and in the null mutant co nfirmed that the RAG3 gene is involved in pyruvate decarboxylase synth esis in K. lactis. The effect is exerted at the mRNA level of the pyru vate decarboxylase structural gene KIPDCA. Despite analogies between t he RAG3 gene of K. lactis and the PDC2 gene of S. cerevisiae, these ge nes were unable to reciprocally complement.