TABLE 2.

Representation of every PTM combination observed on the N terminus of H4 from Xenopus sperm, egg, early embryo, and S3 cultured cells Each row in the table represents a single discrete H4 1–23 peptide species. The left columns indicate the potentially modified residues on each peptide; empty boxes indicate that the residue is unmodified on that species, whereas colored boxes, as annotated in the key at the bottom, show the presence of a particular modification on that species. All observed peptides were acetylated on the N terminus. The relative abundances of each modified peptide species in each histone source are displayed in the final four columns. Isobaric species that do not separate chromatographically are grouped by brackets. Relative abundances between the isobaric species could not be adequately obtained; thus, each unique species within a bracketed group that was observed via ETD/PTR MS/MS is reported as existing at equivalent relative abundance.