Transcription termination factor (PubMed:12626700, PubMed:15845400, PubMed:16648357). Binds promoter DNA and regulates mitochondrial replication and transcription (PubMed:12626700, PubMed:15845400, PubMed:16648357, PubMed:24068965). Transcription termination activity may be polarized with highest termination activity occurring when its DNA-binding site is positioned in the reverse orientation with respect to the incoming RNA polymerase (PubMed:15845400). Required for normal topology and maintenance of mitochondrial DNA (mtDNA) levels (PubMed:24068965). Regulates mtDNA replication by promoting replication pausing, possibly by acting as a natural barrier to replication fork progression (PubMed:24068965). Its function in replication pausing prevents unregulated replication that may occur for example by collisions between the machineries of DNA replication and transcription during mtDNA synthesis (PubMed:24068965). This ensures the incorporation of RNA transcripts into replication intermediates at the replication fork and allow for proper fork progression (PubMed:24068965). Shares mtDNA binding sites with the mitochondrial termination factor mTerf5 and thereby may antagonize mTerf5 function during replication to regulate pausing (PubMed:22784680, PubMed:24068965). Likely to function downstream of Dref which activates genes involved in mtDNA replication and maintenance (PubMed:19032147, PubMed:24068965). Expressed throughout embryogenesis. RNAi-mediated knockdown is lethal. Most mutants fail to develop past the L3 larval stage, and the few pupal escapers do not develop to the late pupal stages. Mitochondrial DNA (mtDNA) copy number fails to increase during larval development and instead steadily decreases. Increase in broken mTDNA replication intermediates. Belongs to the mTERF family.