Fig. 4.

Post-translational modification of CENP-A-associated histone H4. A, Histone H4 peptides and posttranslational modifications identified by LC/MS (ETD) following LysC digestion of CENP-A purified chromatin from asynchronously dividing cells. The absolute amounts of recovered peptides were estimated by comparing peptides to internal standard peptides. B, Full MS spectrum showing the parent ions for histone H4 tails marked by 1–2 acetylations and 0–3 methylations. C, D, H4 S1-R23 tail generated by AspN digestion containing one acetylation and two methylations was fragmented using ETD (25 ms) and observed in an averaged 15 MS2 scans. Acetylation was localized to the N terminus and both methylations were localized to K20.