Methylates MRF1 on 'Gln-287' using S-adenosyl L-methionine as methyl donor. L-glutaminyl-[peptide chain release factor] + S-adenosyl-L-methionine = H(+) + N(5)-methyl-L-glutaminyl-[peptide chain release factor] + S-adenosyl-L-homocysteine Present with 13200 molecules/cell in log phase SD medium. Belongs to the protein N5-glutamine methyltransferase family.