2 AX ▁( H 2 AX ▁ph osph ory l ated ▁on ▁ser ine ▁ 1 3 9 ) ▁can ▁be ▁detected ▁as ▁soon ▁as ▁ 2 0 ▁seconds ▁after ▁ir rad iation ▁of ▁cells ▁( with ▁DNA ▁double - str and ▁break ▁formation ), ▁and ▁half ▁maximum ▁accum ulation ▁of ▁ γ H 2 AX ▁occurs ▁in ▁one ▁minute . ▁ ▁The ▁extent ▁of ▁chrom atin ▁with ▁ph osph ory l ated ▁ γ H 2 AX ▁is ▁about ▁two ▁million ▁base ▁pairs ▁at ▁the ▁site ▁of ▁a ▁DNA ▁double - str and ▁break . ▁▁ γ H 2 AX ▁does ▁not , ▁itself , ▁cause ▁chrom atin ▁de cond ens ation , ▁but ▁within ▁ 3 0 ▁seconds ▁of ▁ir rad iation , ▁R NF 8 ▁protein ▁can ▁be ▁detected ▁in ▁association ▁with ▁ γ H 2 AX . ▁ ▁R NF 8 ▁medi ates ▁extensive ▁chrom atin ▁de cond ens ation , ▁through ▁its ▁subsequent ▁interaction ▁with ▁CH D 4 , ▁a ▁component ▁of ▁the ▁nucle os ome ▁rem od eling ▁and ▁de ac et yl ase ▁complex ▁Nu R D . ▁ ▁After ▁under going ▁relax ation ▁subsequent ▁to ▁DNA ▁damage , ▁followed ▁by ▁DNA ▁repair , ▁chrom atin ▁re co vers ▁to ▁a ▁comp action ▁state ▁close ▁to ▁its ▁pre - dam age ▁level ▁after ▁about ▁ 2 0 ▁min . ▁ ▁Method s ▁to ▁investigate ▁chrom atin ▁▁ ▁Ch IP - seq ▁( Ch rom atin ▁imm un op reci p itation ▁sequ encing ), ▁aim ed