Histone methyltransferase. Preferentially dimethylates 'Lys-4' and 'Lys-27' of histone H3 forming H3K2me2 and H3K27me2. H3 'Lys-4' methylation represents a specific tag for epigenetic transcriptional activation, while 'Lys-27' is a mark for transcriptional repression. L-lysyl(4)-[histone H3] + 2 S-adenosyl-L-methionine = 2 H(+) + N(6),N(6)-dimethyl-L-lysyl(4)-[histone H3] + 2 S-adenosyl-L-homocysteine L-lysyl(27)-[histone H3] + 2 S-adenosyl-L-methionine = 2 H(+) + N(6),N(6)-dimethyl-L-lysyl(27)-[histone H3] + 2 S-adenosyl-L-homocysteine Interacts with BRD4. Belongs to the class V-like SAM-binding methyltransferase superfamily. Histone-lysine methyltransferase family. SET2 subfamily.