H. Klier et al., DETERMINATION AND MUTATIONAL ANALYSIS OF THE PHOSPHORYLATION SITE IN THE HYPUSINE-CONTAINING PROTEIN HYP2P, FEBS letters, 334(3), 1993, pp. 360-364
Electrospray mass spectrometry of the purified isoforms of the hypusin
e-containing protein of Saccharomyces cerevisiae Hyp2p suggested a pho
sphorylation of the acidic isoform, which was confirmed by phosphatase
treatment. The phosphorylation site was mapped to the N-acetylated se
rine residue in position no. 1 by mass spectrometric analysis of enzym
atic fragments. Mutation of this serine residue gives rise to only the
basic isoform, confirming our protein chemical data. As this mutation
has no effect on cell viability or growth rate, the unphosphorylated
isoform is sufficient to exert the essential in vivo function of Hyp2p
.