Double-Stranded Dna-Dependent Atpase Irc3p Is Directly Involved In Mitochondrial Genome Maintenance

Nucleic acid-dependent ATPases are involved in nearly all aspects of DNA and RNA metabolism. Previous studies have described a number of mitochondrial helicases. However, double-stranded DNA-dependent ATPases, including translocases or enzymes remodeling DNA-protein complexes, have not been identified in mitochondria of the yeast Saccha-romyces cerevisae. Here, we demonstrate that Irc3p is a mitochondrial double-stranded DNA-dependent ATPase of the Superfamily II. In contrast to the other mitochondrial Superfamily II enzymes Mss116p, Suv3p and Mrh4p, which are RNA helicases, Irc3p has a direct role in mitochondrial DNA (mtDNA) maintenance. Specific Irc3p-dependent mtDNA metabolic intermediates can be detected, including high levels of double-stranded DNA breaks that accumulate in irc3 Delta mutants. irc3 Delta-related topology changes in rho-mtDNA can be reversed by the deletion of mitochondrial RNA polymerase RPO41, suggesting that Irc3p counterbalances adverse effects of transcription on mitochondrial genome stability.