Major helicase player in mitochondrial RNA metabolism. 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. Involved in the degradation of non-coding mitochondrial transcripts (MT-ncRNA) and tRNA-like molecules. 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. Plays a role in the RNA surveillance system in mitochondria; regulates the stability of mature mRNAs, the removal of aberrantly formed mRNAs and the rapid degradation of non coding processing intermediates. Also implicated in recombination and chromatin maintenance pathways. May protect cells from apoptosis. Associates with mitochondrial DNA. ATP + H2O = ADP + H(+) + phosphate Helicase activity toward DNA substrate is inhibited by micromolar concentrations of 5,6-dichloro-1-(beta-D-ribofuranosyl)benzotriazole (DRBT) and 4,5,6,7-tetrabromobenzotriazole (TBBT). Helicase activity toward RNA substrate is inhibited by elevated concentrations of TBBT. Inhibited by some ring-expanded nucleoside analogs. Homodimer; in free form. Component of the mitochondrial degradosome (mtEXO) complex which is a heteropentamer containing 2 copies of SUPV3L1 and 3 copies of PNPT1. As part of mitochondrial degradosome complex, interacts with GRSF1 in a RNA-dependent manner; the interaction enhances the activity of the complex. Interacts with LAMTOR5/HBXIP, WRN and BLM. Belongs to the helicase family.