A DNA helicase required for maintenance of the functional mitochondrial genome in Saccharomyces cerevisiae

A novel DNA helicase, a homolog of several prokaryotic helicases, including Escherichia coli Rep and UvrD proteins, is encoded by the Saccharomyces ce revisiae nuclear genome open reading frame YOL095c on the chromosome XV. Ou r data demonstrate that the helicase is localized in the yeast mitochondria and is loosely associated with the mitochondrial inner membrane during bio chemical fractionation. The sequence of the C-terminal end of the 80-kDa he licase protein is similar to a typical N-terminal mitochondrial targeting s ignal; deletions and point mutations in this region abolish transport of th e protein into mitochondria. The C-terminal signal sequence of the helicase targets a heterologous carrier protein into mitochondria in vivo. The puri fied recombinant protein can unwind duplex DNA molecules in an ATP dependen t manner. The helicase is required for the maintenance of the functional ([ rho(+)]) mitochondrial genome on both fermentable and nonfermentable carbon sources. However, the helicase is not essential for the maintenance of sev eral defective ([rho(-)]) mitochondrial genomes. We also demonstrate that t he helicase is not required for transcription in mitochondria.