Histone methyltransferase that specifically mono- and dimethylates 'Lys-9' of histone H3 (H3K9me1 and H3K9me2, respectively) in euchromatin. H3K9me represents a specific tag for epigenetic transcriptional repression by recruiting HP1 proteins to methylated histones. Also weakly methylates 'Lys-27' of histone H3 (H3K27me). Also required for DNA methylation, the histone methyltransferase activity is not required for DNA methylation, suggesting that these 2 activities function independently. Probably targeted to histone H3 by different DNA-binding proteins like E2F6, MGA, MAX and/or DP1. During G0 phase, it probably contributes to silencing of MYC- and E2F-responsive genes, suggesting a role in G0/G1 transition in cell cycle. In addition to the histone methyltransferase activity, also methylates non-histone proteins: mediates dimethylation of 'Lys-373' of p53/TP53. Represses the expression of mitochondrial function-related genes, perhaps by occupying their promoter regions, working in concert with probable chromatin reader Baz2b (PubMed:32103178). 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 Methyltransferase activity is inhibited by BIX-01294. Efficiently inhibited by compound E72, a BIX-01294 derivative in which the diazepane ring and the benzyl are replaced with a 3-dimethylaminopropyl and a 5-aminopentyl group at sites B and C, respectively (By similarity). Interacts with WIZ. Part of the E2F6.com-1 complex in G0 phase composed of E2F6, MGA, MAX, TFDP1, CBX3, BAT8, EHMT1, RING1, RNF2, MBLR, L3MBTL2 and YAF2. Interacts with MPHOSPH8 (By similarity). Interacts with CDYL. Interacts with REST only in the presence of CDYL. Part of a complex containing at least CDYL, REST, WIZ, SETB1, EHMT1 and EHMT2 (By similarity). Heterodimer; heterodimerizes with EHMT2. Interacts (via ANK repeats) with RELA (when monomethylated at 'Lys-310'). Interacts with Baz2b (PubMed:32103178). Associates with euchromatic regions. Ubiquitous. The ANK repeats specifically recognize and bind H3K9me1 and H3K9me2 (By similarity). They also specifically recognize and bind RELA subunit of NF-kappa-B, when RELA is monomethylated at 'Lys-310'. The SET domain mediates interaction with WIZ. 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. Embryos die around E9.5. Levels of H3K9me1 and H3K9me2 are drastically reduced. Belongs to the class V-like SAM-binding methyltransferase superfamily. Truncated N-terminus.