Mitochondrial helicase involved in mtDNA replication (PubMed:17272269, PubMed:19063859, PubMed:22952820, PubMed:25023283). Might have a role in mtDNA repair (By similarity). Has DNA strand separation activity needed to form a processive replication fork for leading strand synthesis which is catalyzed by the formation of a replisome complex with POLG and mtSDB (By similarity). Preferentially unwinds DNA substrates with pre-existing 5'-and 3'- single-stranded tails but is also active on a 5'- flap substrate (By similarity). Can dissociate the invading strand of immobile or mobile D-loop DNA structures irrespective of the single strand polarity of the third strand (By similarity). In addition to its DNA strand separation activity, also has DNA strand annealing, DNA strand-exchange and DNA branch migration activities (By similarity). ATP + H2O = ADP + H(+) + phosphate Binds 1 [2Fe-2S] cluster. Homohexamer (via C-terminus) which assembled in a ring-like structure. Homoheptamer which assembled in a ring-like structure. Oligomerization is Mg(2+), nucleotide and DNA-independent, however, Mg(2+) and nucleotide stabilize the homohexameric form. Colocalizes with mtDNA in mitochondrial nucleoids, a nucleoproteins complex consisting of a number of copies of proteins associated with mtDNA, probably involved in mtDNA maintenance and expression. N-terminus enhances protein stability and hexamer formation, which is important for DNA binding, and is required for DNA helicase activity and, ultimately, for mtDNA replisome processivity. The N-terminus contains a putative primase-like domain; however the absence of the zinc binding domain and other motifs important for catalysis suggests that mtDNA-helicase lacks primase activity. Truncated N-terminus.