Carbon catabolite regulation of transcription of nuclear genes coding for mitochondrial proteins in the yeast Kluyveromyces lactis.

Promoter regions of the KlQCR7, KlQCR8 and KlCYC1 genes, coding for subunits of the bc1-complex and cytochrome c respectively, in the short-term Crabtree-negative yeast Kluyveromyces lactis differ markedly in sequence from their Saccharomyces cerevisiae counterparts. They have, however, conserved very similar configurations of binding-site motifs for various transcription factors known to be involved in global and carbon-source regulation in S. cerevisiae. To investigate the carbon source-dependent expression of these genes in K. lactis, we have carried out medium-shift experiments and determined transcript levels during the shifts. In sharp contrast to the situation in S. cerevisiae, the level of expression in K. lactis is not affected when glucose is added to a non-fermentable carbon-source medium. However, the genes are not constitutively expressed, but become significantly induced when the cells are shifted from glucose to a non-fermentable carbon source. Finally, induction of transcriptional activation does not occur in media containing both glucose and non-fermentable carbon sources.