Expression of yeast cytochrome C1 is controlled at the transcriptional level by glucose, oxygen and haem

Abstract

The nuclear gene for cytochrome c1 in Saccharomyces cerevisiae (CYT1) was localized on chromosome XV. Its upstream region was identified by functional complementation. Fusion to the lacZ reporter gene on a CEN plasmid allowed study of the effect of carbon sources and of specific deletion mutations on expression of the gene in yeast transformants. Detailed promoter analysis combined with expression studies in recipient strains defective in regulatory genes identified cis-acting sites and transcription factors involved in the regulated expression of the cytochrome c1 gene. These analyses showed that, in the presence of glucose, transcription of CYT1 is positively controlled by oxygen, presumably through the haem signal, and mediated by the HAP1-encoded transactivator. It is additionally regulated by the HAP2/3/4 complex which mediates gene activation mainly under glucose-free conditions. Basal transcription is, in part, effected by CPF1, a centromere and promoter-binding factor.

Regulation of Mitochondrial Biogenesis in Saccharomyces cerevisiae

“…Specific complexes are formed by ABFl and CPF1, as indicated. meric activator HAP2/3/4 has mainly been carried out using yeast strains mutated in, or lacking one of the three subunits (Bowman et al, 1992;Dorsman and Grivell, 1990;Guarente et al, 1984), often in combination with HAP2/3/4 target sites in artificial promoter-reporter fusions (Forsburg and Guarente, 1988;Keng and Guarente, 1987;Maarse et al, 1988;Oechsner et al, 1992;Trawick et al, 1992). This approach suffers from the serious drawback that such mutants display a pleiotropic petite phenotype that obscures primary effects of the mutations and thus hampers studies of the exact function of the activator complex.…”

“…In the promoters of QCRIO, encoding 8.5-kDa subunit 10 (Brandt et al, 1994), and of CYTI, encoding cytochrome c, (Oechsner et al, 1992;Schneider and Guarente, 1991), a potential low-affinity ABFl target site overlaps a site completely matching the deduced consensus sequence for a high-affinity CPFl-binding site. It is tempting to speculate that modulation of basal and derepressed transcription of CYTI, as inferred from deletion analysis, is exerted by ABF1, and not by CPFl as suggested by the authors (Oechsner et al, 1992). Further analysis is required to investigate the combined action of ABFl and CPFl in regulating biogenesis of the Q C R complex.…”

“…A role for HAP2/3/4 in carbonsource-dependent transcriptional regulation has been demonstrated for the promoter regions of CYTI, encoding cytochrome c , (Oechsner et al, 1992;Schneider and Guarente, 1991) and for QCR2 (Dorsman and Grivell, 1990), QCR7 (De Winde, J. H., unpublished data) and QCR8 (De Winde and Grivell, 1992;Maarse et al, 1988), encoding functionally important structural subunits of the QCR complex (Crivellone et al, 1988;Schoppink, 1989).…”

Growth-regulated formation of heteromeric complexes of the centromere and promoter factor, Cbf1p, in yeast

“…In the UAS region of the CYT1 promoter, recognition elements for Cbf1p (CDE I-like element, GTCACGTG), Hap1p and the Hap2 complex are located on a 100-bp DNA fragment (Oechsner et al 1992;Oechsner and Bandlow 1996). The transactivator protein Hap1p adapts CYT1 expression to aerobic and, to a lesser extent, to anaerobic conditions (Oechsner et al 1992) due to its non-covalent, oxygen-dependent association with heme (Pfeifer et al 1989;Zitomer and Lowry 1992;Ushinsky and Keng 1994). After exhaustion of glucose, the Hap2/3/4/5 complex is assembled (McNabb et al 1994) ± the expression of the transactivating constituent, Hap4p, being negatively controlled by glucose.…”

“…After exhaustion of glucose, the Hap2/3/4/5 complex is assembled (McNabb et al 1994) ± the expression of the transactivating constituent, Hap4p, being negatively controlled by glucose. This complex enhances transcription of CYT1 beyond the level induced by Hap1p alone (Oechsner et al 1992). The Cbf1 protein has been shown to modulate the activation potential of Hap1p during transcriptional adaptation following a switch from anaerobic to aerobic conditions (Oechsner and Bandlow 1996).…”