Saccharomyces cerevisiaepossesses two glycogenin isoforms (designated as Glg1p and Glg2p) that both contain a con-served tyrosine residue, Tyr232. However, Glg2p possesses an additional tyrosine residue, Tyr230 and therefore two potential autoglucosylation sites. Glucosylation of Glg2p was studied using both matrix-assisted laser desorption ionization and electrospray quadrupole time of flight mass spectrometry. Glg2p, carrying a C-terminal (His6) tag, was produced inEscherichia coliand purified. By tryptic diges-tion and reversed phase chromatography a peptide (residues 219–246 of the complete Glg2p sequence) was isolated that contained 4–25 glucosyl residues
