Cloning and molecular analysis of the HAP2 locus: a global regulator of respiratory genes in Saccharomyces cerevisiae.

We report here the cloning of the HAP2 gene, a locus required for the expression of many cytochromes and respiratory functions in Saccharomyces cerevisiae. The cloned sequences were found to direct integration of a marked vector to the chromosomal HAP2 locus, and derivatives of these sequences were shown to yield chromosomal disruptions with a Hap2- phenotype. The gene maps 18 centimorgans centromere proximal to ade5 on the left arm of chromosome VII, distinguishing it from any other previously characterized nuclear petite locus. The HAP2 locus encodes a 1.3-kilobase transcript which is present at extremely low levels and which is derepressed in cells grown in media containing nonfermentable carbon sources. Levels of HAP2 mRNA are not reduced in strains bearing a mutation at the HAP3 locus, which is also required for expression of respiratory functions. Models outlining possible interactions of the products of the HAP2 and HAP3 genes are presented.