Dissection of the promoter of the HAP4 gene in S. cerevisiae unveils a complex regulatory framework of transcriptional regulation.

In S. cerevisiae, the heteromeric Hap2/3/4/5 complex is necessary for induced transcription of a large number of genes involved in oxidative metabolism on non-fermentable carbon sources. The Hap4p subunit is the activator subunit and at the same time also the regulatory part of the complex, since it is the only one whose level is regulated by carbon source itself. HAP4 promoter analysis shows a 265 bp activating region at position -1006/-741 bp upstream of the ATG start codon. Specific and differential protein-binding to a 30 nt CSRE-like sequence within this region was observed with extracts from repressing and inducing carbon sources. Carbon source-dependent activation mediated by the 265 bp fragment, as well as protein binding to the 30 nt CSRE-like region, is dependent on the presence of CAT8 function, unveiling a complex framework by which the expression of the HAP4 gene is coordinated. Copyright 2002 John Wiley & Sons, Ltd.