Binds promoter DNA and regulates initiation of transcription (By similarity). Regulator of mitochondrial ribosome biogenesis and translation that is essential for development (PubMed:16787637, PubMed:23300484). Required for normal mitochondrial transcription and translation (PubMed:16787637, PubMed:23300484). Required for assembly of mitochondrial respiratory complexes and normal mitochondrial function (PubMed:23300484). Maintains 16S rRNA levels and functions in mitochondrial ribosome assembly by regulating the biogenesis of the 39S ribosomal subunit (PubMed:23300484). RNAi-mediated knockdown is pupal lethal. Larvae display a delay in development and a decrease in body size. Display progressive defects in mitochondrial respiratory chain capacity as well as a decrease in the enzyme activity of all mitochondrial oxidative phosphorylation complexes. Decrease in enzyme activity is particularly severe in complex I and IV which also display a decrease in the levels of their assembled complexes. Progressive reduction in 16S rRNA levels and impaired assembly of the large (39S) mitochondrial ribosomal subunit. Increase in mitochondrial DNA (mtDNA) transcription and impaired mitochondrial translation. Belongs to the mTERF family.