Major helicase player in mitochondrial RNA metabolism and maintenance (PubMed:26152302). Likely component of the mitochondrial degradosome (mtEXO) complex, that degrades 3' overhang double-stranded RNA with a 3'-to-5' directionality in an ATP-dependent manner (By similarity). ATPase and ATP-dependent multisubstrate helicase, able to unwind double-stranded (ds) DNA and RNA, and RNA/DNA heteroduplexes in the 5'-to-3' direction (By similarity). Regulates mRNA stability and is required for the correct processing and maturation of mitochondrial transcripts (PubMed:26152302). ATP + H2O = ADP + H(+) + phosphate Unlike in mammals, does not localize to the nucleus. Lethal due to mitochondrial dysfunction. 3 days after egg laying (ael) larvae display a severe decrease in size and a significant increase in mitochondrial mRNA steady-state levels which results in larval lethality by 4 days ael. RNAi-mediated knockdown is pupal lethal. Larvae display significant increases in mitochondrial mRNA and anti-sense RNA steady-state levels but rRNA (12S and 16S) steady-state levels and de novo transcription are not affected. Larvae also display severe decreases in mitochondrial tRNA steady state levels and accumulation of unprocessed precursor transcripts. These defects result in a general decrease in mitochondrial translation and severe decreases in the activity of respiratory chain complexes I, I+III, II+III and IV, whereas the nuclear encoded complex II displays a relatively small decrease. Also displays a small decrease in the peptide steady-state levels of the mitochondrial encoded subunit cox3 and the nuclear encoded subunit ND-30. Belongs to the helicase family.