Binds promoter DNA and regulates initiation of transcription (PubMed:17662942). Required for normal mitochondrial transcription and translation, and for normal assembly of mitochondrial respiratory complexes. Required for normal mitochondrial function (By similarity). Maintains 16S rRNA levels and functions in mitochondrial ribosome assembly by regulating the biogenesis of the 39S ribosomal subunit (By similarity). {ECO:0000250|UniProtKB:Q8R3J4, ECO:0000269|PubMed:17662942}. This is the function of ENSG00000156469 (MTERF3, mitochondrial transcription termination factor 3).