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 mediates monomethylation of 'Lys-56' of histone H3 (H3K56me1) in G1 phase, leading to promote interaction between histone H3 and PCNA and regulating DNA replication. 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. May also methylate histone H1. In addition to the histone methyltransferase activity, also methylates non-histone proteins: mediates dimethylation of 'Lys-373' of p53/TP53. Also methylates CDYL, WIZ, ACIN1, DNMT1, HDAC1, ERCC6, KLF12 and itself. 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 Heterodimer; heterodimerizes with EHMT1/GLP (PubMed:16702210). Interacts with GFI1B and WIZ (PubMed:16688220, PubMed:16702210). 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 (PubMed:12004135). Part of a complex composed of TRIM28, HDAC1, HDAC2 and EHMT2 (PubMed:21549307). Interacts with UHRF1 (PubMed:19056828). Interacts with CDYL (PubMed:19061646). Interacts with REST only in the presence of CDYL (PubMed:19061646). Part of a complex containing at least CDYL, REST, WIZ, SETB1, EHMT1 and EHMT2 (PubMed:19061646). Interacts with PRDM9 and CDYL; interaction only takes place when PRDM9 is bound to hotspot DNA (By similarity). Interacts with SMYD5 (By similarity). Associates with euchromatic regions. Does not associate with heterochromatin. Additional isoforms seem to exist. Expressed in all tissues examined, with high levels in fetal liver, thymus, lymph node, spleen and peripheral blood leukocytes and lower level in bone marrow. The SET domain mediates interaction with WIZ. The ANK repeats bind H3K9me1 and H3K9me2. 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. Methylated at Lys-185; automethylated. Belongs to the class V-like SAM-binding methyltransferase superfamily. Histone-lysine methyltransferase family. Suvar3-9 subfamily. While NG36 and G9a were originally thought to derive from 2 separate genes, all G9A transcripts also contain the in frame coding sequence of NG36. It is uncertain whether Met-1 or Met-21 is the initiator methionine. Extended N-terminus. Extended N-terminus. Truncated N-terminus. Extended N-terminus. Truncated N-terminus.