Mitochondrial peptide chain release factor that directs the termination of translation in response to the peptide chain termination codons UAA and UAG. Methylation of glutamine in the GGQ triplet is conserved from bacteria to mammals (By similarity). N5-methylated on Gln-287 by MTQ1. Present with 414 molecules/cell in log phase SD medium. Belongs to the prokaryotic/mitochondrial release factor family.