Catalysis of the reaction: L-lysyl9- + 2 S-adenosyl-L-methionine = 2 H+ + N6,N6-dimethyl-L-lysyl9- + 2 S-adenosyl-L-homocysteine. This reaction is the successive addition of two methyl groups to the unmethylated lysine residue at position 9 of histone H3, producing histone H3K9me2.
histone H3K9 dimethylation