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RecBCD enzyme is a bipolar DNA helicase.
Mark S Dillingham1, Maria Spies, Stephen C Kowalczykowski
1Section of Microbiology, Center for Genetics and Development, University of California, Davis, California 95616, USA.
Nature
|June 20, 2003
Summary
The Escherichia coli RecBCD enzyme uses two DNA helicases, RecB and RecD, working together in opposite directions. This dual-motor mechanism explains RecBCD
Area of Science:
- Molecular Biology
- Enzymology
- DNA Repair
Background:
- Escherichia coli RecBCD is a key enzyme in DNA repair.
- It processes double-strand breaks for homologous recombination.
- The RecB subunit was known to have 3' to 5' helicase activity.
Purpose of the Study:
- To investigate the helicase activity of the RecD subunit.
- To elucidate the mechanism of DNA unwinding by the RecBCD holoenzyme.
Main Methods:
- Purification of RecD protein.
- Enzyme activity assays with intact and mutated RecBCD.
- DNA translocation and unwinding studies.
Main Results:
- Purified RecD protein exhibits 5' to 3' DNA helicase activity.
- Both RecB and RecD helicases are active in the intact RecBCD enzyme.
- RecBCD remains active for DNA unwinding even when RecB or RecD is mutated.
Conclusions:
- RecBCD functions via a bipolar translocation model.
- Two DNA helicases (RecB and RecD) move in the same direction but with opposite polarities.
- This mechanism explains RecBCD's high speed, processivity, and function in DNA repair.
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