Methyltransferase that catalyzes the formation of N(7)-methylguanine at position 46 (m7G46) in tRNA, a modification required to maintain stability of tRNAs; its absence resulting in tRNA decay. Both the D-stem and T-stem structures of tRNAs are required for efficient methyltransferase activity. guanosine(46) in tRNA + S-adenosyl-L-methionine = N(7)-methylguanosine(46) in tRNA + S-adenosyl-L-homocysteine tRNA modification; N(7)-methylguanine-tRNA biosynthesis. Forms a complex with TRM82. Present with 2630 molecules/cell in log phase SD medium. Belongs to the class I-like SAM-binding methyltransferase superfamily. TrmB family.