Fig. 1.

Characteristics of H3K27me3-K36me2 and H3K27me2-K36me3-containing peptides. a Schematic representation of isobaric pentamethylation of histone H3K27-R40 peptides and their specific ions. b Comigration of H3K27me3-K36me2 and H3K27me2-K36me3-containing peptides on RP-HPLC. Two synthetic isobarically modified peptides of H3K27-R40, S1 (K27me2-K36me3) and S2 (K27me3-K36me2), and their mixtures, M1 (3:1), M2 (1:1), M3 (1:3), and M4 (1:6), were subjected to LC-MS analysis. c Strongest tandem mass spectrum of the M2 sample. Two types of specific y²⁺ ions generated by each isoform were marked with different colors (K27me2-K36me3, red; K27me3-K36me2, green). Quantification was based on the intensity of two types of y11–y13²⁺ ions in the single spectrum. d The intensity of two types of b¹⁺, b²⁺, y¹⁺ and y²⁺ specific ions in a series of tandem mass spectra of M2 was displayed as a chromatographic profile. Quantification was based on the peak area of two types of y11–y13²⁺ ions