Histone methyltransferase that specifically dimethylates histone H3 to form H3K9me2 (PubMed:25533783). H3K9me2 represents a specific tag for epigenetic transcriptional repression by recruiting HP1 proteins to methylated histones (By similarity). Mainly functions in heterochromatin regions, thereby playing a central role in the establishment of constitutive heterochromatin at centromeric regions (Probable). 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 Transcriptionally repressed in an HDA1-dependent manner. In the pre-SET domain, Cys residues bind 3 zinc ions that are arranged in a triangular cluster; some of these Cys residues contribute to the binding of two zinc ions within the cluster. Severely decreases localization of DMT5 to DNA (PubMed:31955845). Decreases methylation of the fifth carbon of cytosine (5mC) in DNA; simultaneous disruption of UHF1 exacerbates the effect (PubMed:31955845). Belongs to the class V-like SAM-binding methyltransferase superfamily. Histone-lysine methyltransferase family. Suvar3-9 subfamily.