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DNA-helicase activity from sea urchin mitochondria
M Roberti1, C Musicco, P L Polosa
1Department of Biochemistry and Molecular Biology, University of Bari, Italy.
Abstract:
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 in Paracentrotus lividus mitochondria. The activity was detected in a protein fraction obtained by fractionating on DEAE-Sephacel a lysate of gradient purified mitochondria from paracentrotus lividus eggs. 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 Escherichia coli rep helicase 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.
Insights
Researchers identified a novel DNA helicase in sea urchin mitochondria. This enzyme unwinds DNA, suggesting a role in mitochondrial DNA replication and H-strand polymerization.
Area of Science:
- Molecular Biology
- Biochemistry
- Genetics
Background:
- Mitochondrial DNA replication is crucial for cellular energy production.
- Understanding the protein components of mitochondrial DNA replication is essential.
- Sea urchins (Paracentrotus lividus) serve as a model organism for studying developmental processes.
Purpose of the Study:
- To characterize key components of the sea urchin mitochondrial DNA replication machinery.
- To identify and analyze DNA helicase activity within Paracentrotus lividus mitochondria.
Main Methods:
- Isolation and purification of mitochondria from sea urchin eggs.
- Fractionation of mitochondrial lysate using DEAE-Sephacel chromatography.
- Assay of DNA helicase activity using a synthetic DNA substrate (oligonucleotide annealed to M13mp18 DNA).
Main Results:
- A DNA helicase activity was detected in a protein fraction from Paracentrotus lividus mitochondria.
- The identified helicase unwound a 39-base oligonucleotide annealed to single-stranded DNA in the presence of ATP and Mg++.
- The enzyme exhibited a 3' to 5' directionality on the single-stranded DNA portion of the substrate.
Conclusions:
- The characterized sea urchin mitochondrial helicase shares functional similarities with known helicases (e.g., E. coli rep helicase, bovine brain mitochondrial helicase).
- This enzyme's polarity suggests a potential role in facilitating H-strand polymerization during sea urchin mitochondrial DNA replication.