REGULATION OF MITOCHONDRIAL BIOGENESIS IN SACCHAROMYCES-CEREVISIAE - INTRICATE INTERPLAY BETWEEN GENERAL AND SPECIFIC TRANSCRIPTION FACTORSIN THE PROMOTER OF THE QCR8 GENE

Transcription of the QCR8 gene, encoding subunit VIII of the Saccharom yces cerevisiae mitochondrial ubiquinol-cytochrome c oxidoreductase (Q CR), is controlled by the carbon-source-dependent heme-activator prote in complex HAP2/3/4 and the general transcriptional regulators autonom ous replication-site-binding factor ABF1 and centromere-binding and pr omoter-binding factor CPF1. In this study, we investigate and dissect the relative contributions and mutual interactions of these regulators in transcriptional control. Transcription was analyzed both under ste ady-state conditions and during nutritional shifts, in hap Delta mutan ts and after site-specific mutagenesis of the various binding sites in the chromosomal context of the QCR8 gene. We present evidence for bot h direct and indirect interactions between ABF1 and HAP2/3/4, and show that HAP2/3/4 is essential for a rapid transcriptional induction duri ng transition from repressed to derepressed conditions. However, the a ctivator is not the only determinant for carbon-source-dependent regul ation, and we observe a functional difference between HAP2/3/4 and the HAP2/3 subcomplex. ABF1 is required for maintainance of basal repress ed and derepressed. transcription in the steady state of growth. The r epressive action of the negative modulator CPF1 during escape from glu cose repression is overcome through the cooperative action of ABF1 and HAP2/3/4. The implications of the intricate interactions of these DNA -binding regulators for control of expression of mitochondrial protein genes are discussed.