Histone methyltransferase. Methylates 'Lys-9' of histone H3. H3 'Lys-9' methylation represents a specific tag for epigenetic transcriptional repression. N(6)-methyl-L-lysyl(9)-[histone H3] + S-adenosyl-L-methionine = H(+) + N(6),N(6)-dimethyl-L-lysyl(9)-[histone H3] + S-adenosyl-L-homocysteine L-lysyl(9)-[histone H3] + S-adenosyl-L-methionine = H(+) + N(6)-methyl-L-lysyl(9)-[histone H3] + S-adenosyl-L-homocysteine Associates with centromeric constitutive heterochromatin. Although the SET domain contains the active site of enzymatic activity, both pre-SET and post-SET domains are required for methyltransferase activity. Cys residues in the pre-SET domain normally bind 3 zinc ions that are arranged in a triangular cluster, but here these Cys residues are only partially conserved, suggesting that the pre-Set domain may not bind a zinc cluster. Belongs to the class V-like SAM-binding methyltransferase superfamily. Histone-lysine methyltransferase family. Suvar3-9 subfamily.