Binds promoter DNA and regulates initiation of transcription (By similarity). Required for normal mitochondrial transcription and translation, and for normal assembly of mitochondrial respiratory complexes (PubMed:17662942, PubMed:23300484). Required for normal mitochondrial function (PubMed:17662942, PubMed:23300484). Maintains 16S rRNA levels and functions in mitochondrial ribosome assembly by regulating the biogenesis of the 39S ribosomal subunit (PubMed:17662942, PubMed:23300484). Contains seven structural repeats of about 35 residues, where each repeat contains three helices. The repeats form a superhelical structure with a solenoid shape. Embryonic lethality, due to severe mitochondrial dysfunction. Embryos are much smaller than normal and none survive past 10.5 dpc. Belongs to the mTERF family.