THE HYP2 GENE OF SACCHAROMYCES-CEREVISIAE IS ESSENTIAL FOR AEROBIC GROWTH - CHARACTERIZATION OF DIFFERENT ISOFORMS OF THE HYPUSINE-CONTAINING PROTEIN HYP2P AND ANALYSIS OF GENE DISRUPTION MUTANTS

In Saccharomyces cerevisiae, hypusine-containing proteins are encoded by two closely related genes, HYP1 and HYP2, which are regulated recip rocally by oxygen and heme. We have purified the aerobically expressed hypusine-containing proteins from yeast. The three proteins detected (two isoforms, which differ in their pI values, and a degradation prod uct thereof, lacking the N-terminal 10 amino acid residues) are all en coded by HYP2. The N-terminus of both isoforms is formed by acetylatio n of a serine residue after cleavage of the first methionine. Cells mu tant for hyp2 are unable to grow aerobically. However, under anaerobic conditions these mutants display no obvious phenotype, presumably bec ause the strictly anaerobically expressed HYP1 gene product (Hyp1p) is present. This implies that Hyp1p and Hyp2p fulfill very similar funct ions. In fact, Hyp1p can substitute for Hyp2p under aerobic conditions , when expressed under the control of the GAL1 promoter in hyp2 mutant cells.