The function of MTRF1 (mitochondrial translation release factor 1, Ensembl gene identifier ENSG00000120662) is as follows. Mitochondrial peptide chain release factor that directs the termination of translation in response to the peptide chain non- canonical stop codons AGG and AGA (PubMed:36302763, PubMed:36596788, PubMed:37141370). Non-canonical termination codons AGG and AGA are found at the end of MT-CO1/COX1 and MT-ND6/ND6 open reading frames, respectively (PubMed:37141370). Recognizes non-canonical stop codons via a network of interactions between the codon, MTRF1 and the ribosomal RNA (rRNA): in contrast to other translation release factors, which identify the codon in the A-site via direct interactions of amino acid side chains with the bases, MTRF1 repositions the first 2 bases of the stop codon to use an intricate network of interactions that includes residues of the release factor, the rRNA of the small ribosomal subunit, as well as neighboring bases of the mRNA (PubMed:37141370). {ECO:0000269|PubMed:36302763, ECO:0000269|PubMed:36596788, ECO:0000269|PubMed:37141370}.