Sequence and nuclear localization of the Saccharomyces cerevisiae HAP2 protein, a transcriptional activator.

Activation of the CYC1 upstream activation site (UAS2) and other Saccharomyces cerevisiae genes encoding respiratory functions requires the products of the regulatory loci HAP2 and HAP3. We present here the DNA sequence of the yeast HAP2 gene and an initial investigation into the function of its product. The DNA sequence indicated that HAP2 encoded a 265-amino-acid protein whose carboxyl third was highly basic. Also found in the sequence was a polyglutamine tract spanning residues 120 to 133. Several experiments described herein suggest that HAP2 encodes a direct activator of transcription. First, a bifunctional HAP2-beta-galactosidase fusion gene was localized to the yeast nucleus. Second, a lexA-HAP2 fusion gene was capable of activating transcription when bound to a lexA operator site. The additional requirement for the HAP3 product in activation is discussed.