Reaction catalyzed by [histone H3]-lysine27 N-trimethyltransferase (2.1.1.356)

		+		[histone H3]-N6,N6-dimethyl-L-lysine27	=			+
	S-adenosyl-L-methionine	+		[histone H3]-N6,N6-dimethyl-L-lysine27	=		S-adenosyl-L-homocysteine	+		[histone H3]-N6,N6,N6-trimethyl-L-lysine27