Regulation of the Saccharomyces cerevisiae DLD1 gene encoding the mitochondrial protein D-lactate ferricytochrome c oxidoreductase by HAP1 and HAP2/3/4/5

Expression of the nuclear gene encoding the mitochondrial enzyme D-lactate ferricytochrome c oxidoreductase (D-LCR) was investigated in Saccharomyces cerevisiae. This gene (DLD1) was found to be subject to several regulatory controls at the transcriptional level: synthesis of DLD1 mRNA is repressed by glucose, is derepressed in ethanol or lactate and is heme dependent. We therefore examined the role of the heme-dependent transcriptional activator Hap1p and the carbon source-dependent Hap2/3/4/5 complex. We found that th e Hap2/3/4/5 complex and Hap1p have additive effects on the activation of D LD1 transcription: the Hap2/3/4/5 complex is necessary for DLD1 derepressio n following a shift from fermentable to non-fermentable carbon sources, whi le the Hap1p effect was independent of the carbon sources tested. An upstre am region required for expression and regulation of the DLD1 gene was ident ified. Within this region the binding sites for both the Hap2/3/4/5 complex and Hap1p were defined by gel retardation experiments and site-directed mu tagenesis. Comparison between sequences recognized by Hap1p in different pr omoters showed that the Hap1p binding site in the DLD1 promoter diverges fr om the consensus Hap1p binding site.