Methylates the class 1 translation termination release factors RF1/PrfA and RF2/PrfB on the glutamine residue of the universally conserved GGQ motif. Catalyzes the formation of N(7)-methylguanine at position 46 (m7G46) in tRNA. L-glutaminyl-[peptide chain release factor] + S-adenosyl-L-methionine = H(+) + N(5)-methyl-L-glutaminyl-[peptide chain release factor] + S-adenosyl-L-homocysteine guanosine(46) in tRNA + S-adenosyl-L-methionine = N(7)-methylguanosine(46) in tRNA + S-adenosyl-L-homocysteine In the C-terminal section; belongs to the class I-like SAM-binding methyltransferase superfamily. TrmB family. In the N-terminal section; belongs to the protein N5-glutamine methyltransferase family. PrmC subfamily.