Figure 7.

Histone 3 lysine ethylation is a novel posttranslational modification. A, B) Representative MS/MS spectra and ion tables of the unmodified (A) and the ethylated (B) peptide KSAPATGGVKKPHR. B₁₀-b₁₃ ions and y₅-y₁₃ ions demonstrate the ethylation of K10 (+33 Da). C) N-terminal sequence of histone 3. Black letters mark peptides with identified lysine ethylation and red Ks mark the localization of the modified lysines. Lower panels: Quantitation of peptides containing ethionine-d₅. Histone 3 peptides were from THP-1 cells grown in the presence of 2.5 mM ethionine or ethionine-d₅ for 48 h.