Non-catalytic component of a methyltransferase complex required for the formation of N(7)-methylguanine in a subset of RNA species, such as tRNAs, mRNAs and microRNAs (miRNAs). In the methyltransferase complex, it is required to stabilize and induce conformational changes of the catalytic subunit. Required for the formation of N(7)-methylguanine at position 46 (m7G46) in tRNA. Also required for the formation of N(7)-methylguanine at internal sites in a subset of mRNAs. Also required for methylation of a specific subset of miRNAs. tRNA modification; N(7)-methylguanine-tRNA biosynthesis. Forms a heterodimer with the catalytic subunit mettl1. Belongs to the WD repeat TRM82 family.