Table 2. Summary of overrepresented motifs at PTM sites.

PTM	Motif	Motif in literature	Binding motif in literature
pS	.....sP....	ERK1, ERK2 Kinase substrate motif	WW domain binding motif
pS	.E…s.....	Unknown	Unknown
pT	...E.t.....	Unknown	Unknown
Kac	.....kA..K.	Enrichment for small residues [1], k...K, K...k [2]	In yeast, Gcn5 binds to the H3 peptide K-S-T-G-G-K-A-P-R-K-Q [3]
Kac	.....k..S..	Enrichment for phosphorylatable residues [1]	H3K14 acetylation by Gcn5 is increased when H3S10 is phosphorylated [4]
Kac	....Gk...K.	Gk [5], [6], Enrichment for small residues [1], k...K, K...k [2]	In yeast, Gcn5 binds to the H3 peptide K-S-T-G-G-K-A-P-R-K-Q [3]
Kme	.....k...R.	RG-rich motif [7], [8]	Unknown
Kme	.....kG....	RG-rich motif [7], [8]	Unknown
Kme	.....k..S..	Serine at +2 position [8]	Unknown
Kme	...G.k.....	RG-rich motif [7], [8]	Unknown

A total of ten motifs were detected, flanking either acetylation, methylation or phosphorylation sites. For each motif, bibliographic references for the same or similar motifs are listed, as well as whether it is known to function as a binding motif. Unknown motifs were novel at the time of writing. Many of the identified motifs are novel and distinct from human motifs in the human protein reference database (HPRD). In support of our dataset many of the sites also matched known motifs for the enzymes that catalyse these PTMs, and/or known binding motifs that require modified residues.