Catalyzes the S-adenosyl-L-methionine-dependent formation of N(1)-methyladenine at position 58 (m1A58) in tRNA. Is required for cell growth at extreme temperatures. adenosine(58) in tRNA + S-adenosyl-L-methionine = H(+) + N(1)-methyladenosine(58) in tRNA + S-adenosyl-L-homocysteine Homotetramer composed of a dimer of dimers. Contains a large catalytic C-terminal domain that binds S-adenosyl-L-methionine and a smaller N-terminal domain that may play a role in tRNA recognition. Domains are connected by a linker region. Belongs to the class I-like SAM-binding methyltransferase superfamily. TRM61 family.