N(6),N(6),N(6)-trimethyl-L-lysyl(27)-[histone H3] + S-adenosyl-L-homocysteine + H(+) => N(6),N(6)-dimethyl-L-lysyl(27)-[histone H3] + S-adenosyl-L-methionine
n(6),n(6),n(6)-trimethyl-l-lysyl(27)-[histone h3] + s-adenosyl-l-homocysteine + h(+) => n(6),n(6)-dimethyl-l-lysyl(27)-[histone h3] + s-adenosyl-l-methionine