DNA-Helicase Activity from Sea Urchin Mitochondria

As a step toward the characterization of the main components of mitochondrial DNA replication apparatus in sea urchin, we report the identification of a DNA-helicase activity inParacentrotus lividusmitochondria. The activity was detected in a protein fraction obtained by fractionating on DEAE-Sephacel a lysate of gradient purified mitochondria fromParacentrotus lividuseggs. The mitochondrial helicase unwound, in the presence of ATP and Mg++, a 39-base oligonucleotide annealed to single-stranded M13mp18 (+) DNA. Its direction of movement is 3′ to 5′ with respect to the single stranded portion of the partial duplex DNA substrate. This polarity is similar to that exhibited by the single stranded portion of the partial duplex DNA substrate. This polarity is similar to that exhibited by theEscherichia coli rephelicase and by the helicase from bovine brain mitochondria. These features suggest that the sea urchin mitochondrial helicase could function in enabling the polymerization of the H-strand during mitochondrial DNA replication.