Acetylation of lysine residues in proteins plays a key role in modulating biological activities. For example, acetylation of histones, the protein spools for DNA in cells, helps regulate gene expression. Acetylation is typically detected by radiolabeling techniques, but researchers at Rockefeller University are now reporting a faster, safer method for identifying proteins that undergo this posttranslational modification (J. Am. Chem. Soc., DOI: 10.1021/ja908871t). Yu-Ying Yang, Janice M. Ascano, and Howard C. Hang developed alkyne analogs of acetyl-CoA that serve as substrates for lysine acetyltransferases—the enzymes that acetylate proteins—and act as chemical reporters of protein acetylation. After an analog has been incorporated into a protein, the researchers use a Cu(I)-catalyzed azide-alkyne cycloaddition reaction, a so-called click reaction, to install either a fluorescent label for imaging analysis or a biotin tag for affinity purification and subsequent mass spectrometric analysis. The team used the reporter to identify known and previously unknown acetylated proteins. The method should be useful for large-scale analysis of protein acetylation and for identifying protein substrates in complex mixtures, the authors note.