Methylates the class 1 translation termination release factors RF1/PrfA and RF2/PrfB on the glutamine residue of the universally conserved GGQ motif, i.e. on 'Gln-235' in RF1 and on 'Gln-252' in RF2. L-glutaminyl-[peptide chain release factor] + S-adenosyl-L-methionine = H(+) + N(5)-methyl-L-glutaminyl-[peptide chain release factor] + S-adenosyl-L-homocysteine Interacts with PrfA and PrfB. Cells lacking this gene suffer severe growth defects, but also show a global shift in gene expression to anaerobic respiration. Also shows defects in translational termination via an enhanced rate of read-through of nonsense codons and induction of transfer-mRNA-mediated tagging of proteins within the cell. Belongs to the protein N5-glutamine methyltransferase family. PrmC subfamily. Was originally thought to be involved in the oxidation of protoporphyrinogen into protoporphyrin IX.