Regulator of mitochondrial ribosome biogenesis and translation. Binds to mitochondrial ribosomal RNAs 16S, 12S and 7S and targets NSUN4 RNA methyltransferase to the mitochondrial large ribosomal subunit (39S). . This is the function of MTERF4 (mitochondrial transcription termination factor 4, Ensembl gene identifier ENSG00000122085).