Catalytic subunit of tRNA (adenine-N(1)-)-methyltransferase, which catalyzes the formation of N(1)-methyladenine at position 58 (m1A58) in initiator methionyl-tRNA. Catalytic subunit of mRNA N(1)-methyltransferase complex, which mediates methylation of adenosine residues at the N(1) position of a small subset of mRNAs: N(1) methylation takes place in tRNA T-loop-like structures of mRNAs and is only present at low stoichiometries. adenosine(58) in tRNA + S-adenosyl-L-methionine = H(+) + N(1)-methyladenosine(58) in tRNA + S-adenosyl-L-homocysteine an adenosine in mRNA + S-adenosyl-L-methionine = an N(1)-methyladenosine in mRNA + H(+) + S-adenosyl-L-homocysteine Heterotetramer; composed of two copies of TRMT6 and two copies of TRMT61A. Belongs to the class I-like SAM-binding methyltransferase superfamily. TRM61 family.