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 encodi ng subunit VII of the mitochondrial bc(1) complex of the yeast Kluyver omyces 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 an d QCR7 genes is conserved between S. cerevisiae and K. lactis. The int ergenic regions containing the QCR7 promoters of the two yeasts, diffe r significantly in length and lack overall DNA sequence similarity, bu t they do share a binding site for the transcription factor complex HA P2/3/4. The KIQCR7 promoter contains, in addition, a CPF1 consensus bi nding site which is absent from ScQC7. Deletion of a 35 bp region cont aining these two sites severely lowers the mRNA expression during grow th on both glucose and ethanol/glycerol, but growth rate on both carbo n sources is only mildly affected. Interestingly, in respect to the KI QCR7 gene, KlCPF1 seems to act as an important transcriptional activat or, thus contrasting the proposed repressor function of ScCPF1 for the ScQCR8 gene of S. cerevisiae.