FIGURE 3.

PRDM7 selectively trimethylates H3K4me2. Methylation of H3(1–25) peptides or H3(21–44) peptides by (A) wild-type PRDM7 (1 μm) or (B) S357Y PRDM7 (0.1 μm) as determined by LC-MS-TOF. Spectra shown are the m/z signal for the +5-charged peptides. Initial K4 methylation states of the substrate peptide are marked on the left side and the expected m/z range for the various product methylation states are indicated at the top. For H3K36me2 methylation by PRDM7 S357Y additional peaks corresponding to the addition of 2 or 3 methyl groups was also observed (indicated by arrows). Data are presented as a representative single trace from a series of at least three independent experiments.