Dimethylates a single guanine residue at position 26 of most tRNAs using S-adenosyl-L-methionine as donor of the methyl groups. Required for the modification of both mitochondrial and cytoplasmic tRNAs. guanosine(26) in tRNA + 2 S-adenosyl-L-methionine = 2 H(+) + N(2)-dimethylguanosine(26) in tRNA + 2 S-adenosyl-L-homocysteine Predominantly targeted to the nucleus. Isoform 2 is N-acetylated by NatC at position 1. N-acetylation is necessary for targeting of the protein to the inner nuclear membrane. Present with 15500 molecules/cell in log phase SD medium. Belongs to the class I-like SAM-binding methyltransferase superfamily. Trm1 family.