Table 1.

Transcripcion-associated covalent histone modifications

Residue	Modification	Relation with gene expression	Localization
Histone H3
K4	me1	Inactive or active [74]	Widespread[75]; Enhancers[74, 76]
	me2	Active[77, 78]	TSS[75]
	me3	Active[75–80]; Inactive(Poised)[81, 82]	TSS[75, 76, 80]
R8	Me	Inactive [83, 84]
K9	Ac	Active[75, 77, 79, 80, 85–87]	TSS[75, 80, 85]
	me3	Inactive[79, 82, 88, 89]	Heterochromatin [90]
S10	P	Active[91, 92]	TSS [92]
K14	Ac	Active[75, 77, 85–87]	TSS[75, 85]
K16	Ac	Active[79]
R17	me1/me2-asym	Active [93]
K18	Ac	Active[87, 93]
K20	me1	Inactive [88]
K23	Ac	Active[87, 93]
K27	Ac	Active [74]	Enhancer [74]
	me3	Inactive[79, 81, 82, 88, 89]
K36	me3	Active[80, 82, 85]; Hallmark of elongation[79, 85]	Coding[80]
K79	me1	Inactive[94]	TSS or Intergenic[94]
	me2	Active[94]	Coding[80]; TSS[94]
	me3	Active[94]	TSS[94]
Histone H4
R3	me2 (sym)	Inactive[83, 95, 96]	TSS[95]
K5/K8/K12/K16	Ac	Active[78]	Widespread[75]
K20	me3	Inactive [82]

Abbreviations: ac: acetylation; K: lysine residues; me: methylation, where me1, 2, 3 denotes mono-, di-, or trimethylation; P: phosphorylation; R: arginine residue; (a) sym: (a) symmetrical; TSS: Transcription Start Site