ISOLATION AND CHARACTERIZATION OF THE LINKED GENES APA2 AND QCR7, CODING FOR AP(4)A PHOSPHORYLASE-II AND THE 14-KDA SUBUNIT-VII OF THE MITOCHONDRIAL BC(1)-COMPLEX IN THE YEAST KLUYVEROMYCES-LACTIS

We report the isolation and characterization of the KlQCR7 gene encoding subunit VII of the mitochondrial bc(1) complex of the yeast Kluyveromyces lactis. The coding region is 69.3% identical to its counterpart in Saccharomyces cerevisiae (ScQCR7). Like the KlQCR8 gene (Mulder et al., accompanying paper) expression of the KlQCR7 gene during growth on glucose is high and can be further induced when cells are grown on non-fermentable carbon sources. The chromosomal linkage of the APA2 and QCR7 genes is conserved between S. cerevisiae and K. lactis. The intergenic regions containing the QCR7 promoters of the two yeasts, differ significantly in length and lack overall DNA sequence similarity, but they do share a binding site for the transcription factor complex HAP2/3/4. The KIQCR7 promoter contains, in addition, a CPF1 consensus binding site which is absent from ScQC7. Deletion of a 35 bp region containing these two sites severely lowers the mRNA expression during growth on both glucose and ethanol/glycerol, but growth rate on both carbon sources is only mildly affected. Interestingly, in respect to the KIQCR7 gene, KlCPF1 seems to act as an important transcriptional activator, thus contrasting the proposed repressor function of ScCPF1 for the ScQCR8 gene of S. cerevisiae.