| DNA PKcs alone catalyzed DNA dependent phosphorylation at a very low but significant level , and HMG 1 and 2 markedly stimulated the phosphorylation of alpha casein and a specific peptide substrate in a DNA dependent manner . ^^^ Anti ( Ku protein ) antibodies inhibited the DNA dependent phosphorylation activity of the DNA PKcs : Ku protein complex , but not that of DNA PKcs alone or when it was complexed with HMG 1 or 2 . ^^^ These results demonstrate that HMG 1 and 2 can function as the DNA binding regulatory component for DNA PKcs in vitro , and imply that a conformational change of dsDNA , which is elicited by regulatory components , is important for the stimulation of DNA PK activity of DNA PKcs . . ^^^ |