Fig. 2. Label-free semi-quantification of modification on histone H4 tail during the cell cycle.

(a) Cell cycle synchronization: HeLa S3 cells were synchronized by double thymidine blocking and collected at two-hour intervals after release. Cell cycle synchrony was confirmed by flow cytometry. (b) Hierarchical clustering of temporal changes in abundance of modifications during the cell cycle: Ion abundances of +4 ion peaks were summed and normalized to the maximum abundance (shown in columns) of each species. Representative modifications for the peaks are selected as annotation from Table S2. Peaks whose PTM assignment showed conflicts between datasets were written in italics. Peak number in bold red indicates S1ph containing species.