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The directionality of RuvAB-mediated branch migration: in vitro studies with three-armed junctions
K Hiom1, I R Tsaneva, S C West
1Imperial Cancer Research Fund, Clare Hall Laboratories, South Mimms, Hertfordshire, UK.
Summary
The Escherichia coli RuvAB complex facilitates unidirectional branch migration of three-armed DNA junctions. This process is dictated by the asymmetric binding of RuvA and RuvB proteins, guiding DNA through a single RuvB ring.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Escherichia coli RuvA and RuvB proteins are key players in genetic recombination.
- They facilitate branch migration of Holliday junctions, involving a complex of RuvA bound to DNA and two RuvB hexameric rings.
- Branch migration is an ATP-dependent process where DNA translocates through RuvB rings.
Purpose of the Study:
- To elucidate the mechanism of RuvAB-catalyzed branch migration on three-armed (Y) DNA junctions.
- To understand the role of protein assembly and DNA structure in determining reaction polarity.
Main Methods:
- Utilized synthetic DNA structures to study branch migration.
- Employed DNase footprinting to analyze the RuvAB-junction complex structure.
- Characterized DNA products to determine reaction polarity.
Main Results:
- Observed unidirectional branch migration of Y-junctions, producing specific DNA products.
- RuvA binds asymmetrically to the DNA junction.
- A single RuvB hexameric ring is targeted to one arm of the DNA by RuvA.
Conclusions:
- Branch migration of Y-junctions is unidirectional, controlled by the assembly of one RuvB ring on a specific DNA arm.
- The asymmetric complex formation dictates the directionality of branch migration.
- Strand passage, coupled with DNA unwinding, occurs as DNA is processed through the RuvB ring.