▁mot if ▁‘ S Q ( E / D ) Φ ’ ▁( where ▁ Φ - re pres ents ▁a ▁hydro ph ob ic ▁resid ue , ▁usually ▁T yr ▁in ▁m amm als ). ▁It ▁becomes ▁ph osph ory l ated ▁during ▁the ▁DNA ▁damage ▁response , ▁chrom atin ▁rem od eling , ▁and ▁X - chrom os ome ▁in activ ation ▁in ▁som atic ▁cells . ▁H 2 A . X ▁and ▁canonical ▁H 2 A ▁have ▁diver ged ▁several ▁times ▁in ▁ph y log en etic ▁history , ▁but ▁each ▁H 2 A . X ▁version ▁is ▁character ized ▁by ▁similar ▁structure ▁and ▁function , ▁suggesting ▁it ▁may ▁represent ▁the ▁ancest ral ▁state . ▁H 2 A . Z ▁regul ates ▁trans cription , ▁DNA ▁repair , ▁supp ression ▁of ▁ant is ense ▁R NA , ▁and ▁R NA ▁Pol ym er ase ▁II ▁rec ruit ment . ▁Notable ▁features ▁of ▁H 2 A . Z ▁include ▁a ▁sequence ▁mot if ▁‘ DE ELD ,’ ▁a ▁one ▁am ino ▁acid ▁insert ion ▁in ▁L 1 - loop , ▁and ▁a ▁one ▁am ino ▁acid ▁delet ion ▁in ▁the ▁dock ing ▁domain ▁relative ▁to ▁canonical ▁H 2 A . ▁Vari ant ▁H 2 A . Z . 2 ▁was ▁suggested ▁to ▁be ▁driving ▁the ▁pro gression ▁of ▁m align ant ▁mel an oma . ▁Can on ical ▁H 2 A ▁can ▁be ▁ex changed ▁in ▁nucle os om es ▁for ▁H 2 A . Z ▁with ▁special ▁rem od eling