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 VI II of the mitochondrial ubiquinol cytochrome c oxidoreductase, is subj ect to glucose repression, whereas in the distantly related yeast Kluy veromyces lactis it is not. The homologous promoter regions lack overa ll DNA-sequence identity, but do share binding sites for the transcrip tion factors Abf1p, Cpf1p and Hap2/3/4p. For S. cerevisiae it has been established that these factors are involved in growth and carbon sour ce control of nuclear genes encoding mitochondrial proteins. Here we p resent experimental evidence that K. lactis counterparts of Abf1p and Cpf1p bind independently to the KIQCR8 promoter. The presence of the K IHap2/3/4p binding site enhances binding of KIAbf1p, strongly suggesti ng that the KIHap2/3/4p complex stabilizes binding of KIAbf1p. In reci procal 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 l actis, distinct from Abf1p, Cpf1p and Hap2/3/4p, are able to activate transcription of the QCR8 gene during both fermentative and nonferment ative growth, as well as to induce transcription during growth on non- fermentable carbon sources. In both yeasts, Abf1p is involved in trans criptional activation under both fermentative and nonfermentative grow th conditions. Hap2/3/4p plays a minor activational role during fermen tative growth, hut is mainly responsible for transcriptional induction under non-fermentative growth conditions. Under these latter conditio ns Abf1p and Hap2/3/4p activate transcription synergistically.