. "\"The modification of histone H2A by the addition of an phosphate group to a serine residue at position 139 of the histone.\" [GOC:yaf, PMID:16061642]" . . "histone H2A-S139 phosphorylation" . "Residue 1 of histone H2AX is taken as the first residue following removal of the initiating Methionine (Met)." . . "histone H2A.x phosphorylation at S139" .