Distinct transcriptional regulation of a gene coding for a mitochondrial protein in the yeasts Saccharomyces cerevisiae and Kluyveromyces lactis despite similar promoter structures.

In Saccharomyces cerevisiae transcription of QCR8, encoding subunit VIII of the mitochondrial ubiquinol cytochrome c oxidoreductase, is subject to glucose repression, whereas in the distantly related yeast Kluyveromyces lactis it is not. The homologous promoter regions lack overall DNA-sequence identity, but do share binding sites for the transcription factors Abf1p, Cpf1p and Hap2/3/4p. For S. cerevisiae it has been established that these factors are involved in growth and carbon source control of nuclear genes encoding mitochondrial proteins. Here we present experimental evidence that K. lactis counterparts of Abf1p and Cpf1p bind independently to the KIQCR8 promoter. The presence of the KIHap2/3/4p binding site enhances binding of KIAbf1p, strongly suggesting that the KIHap2/3/4p complex stabilizes binding of KIAbf1p. In reciprocal exchanges of the QCR8 genes between S. cerevisiae and K. lactis, overall regulation of transcription was found to be species specific. In contrast to S. cerevisiae, additional elements and factors in K. lactis, distinct from Abf1p, Cpf1p and Hap2/3/4p, are able to activate transcription of the QCR8 gene during both fermentative and non-fermentative growth, as well as to induce transcription during growth on non-fermentable carbon sources. In both yeasts, Abf1p is involved in transcriptional activation under both fermentative and non-fermentative growth conditions. Hap2/3/4p plays a minor activational role during fermentative growth, but is mainly responsible for transcriptional induction under non-fermentative growth conditions. Under these latter conditions Abf1p and Hap2/3/4p activate transcription synergistically.