Method identifies histone modifications

Post-translational modifications (PTMs) of histones—the protein spools that DNA is wound around—help regulate gene expression. Figuring out whether combinations of these PTMs make up a histone code has been difficult because of the challenge of determining multiple PTMs simultaneously. The H3 histone has such a complicated PTM pattern that analyzing intact proteins via high-resolution mass spectrometry (MS) has been insufficient for characterization. Craig A. Mizzen, Neil L. Kelleher, and coworkers at the University of Illinois, Urbana-Champaign, deal with the complexity by combining hydrophilic interaction chromatography (HILIC) with Fourier transform MS of only the first 50 residues of H3, where most of the known modification sites are located (Nat. Methods, DOI: 10.1038/nmeth1052). HILIC separates the histone subtypes first according to the degree of acetylation and then by the degree of methylation. The researchers identified more than 150 combinations of PTMs on one type of histone H3 found in human cancer cells. Many of these combinations had not been seen previously.