Fig. 1.

Sources of discrepancy in H3K4 quantitation. A, Equimolar mixture of isotope-labeled, propionylated H3 T3-R8 peptide in eight modification states, injected in the milieu of endogenous histones from 293T cells. B, Time course of digestion releasing propionylated H3 T3-R8 from propionylated H3 A1-R17, where K4 is trimethylated. C, Relative ionization efficiencies of the propionylated H3 T3-R8 peptide in its various modified forms. D, Recovery of H3 T3-R8 peptides following StageTip C18 cleanup. In panels A, C, D, all abundances are expressed relative to the unmodified peptide.