RuvAB-mediated branch migration does not involve extensive DNA opening within the RuvB hexamer

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Escherichia coli RuvA and RuvB proteins are essential for homologous recombination and DNA repair.
• These proteins mediate the branch migration of Holliday junctions, a critical step in DNA repair.
• The RuvAB complex, with RuvA binding the junction and RuvB hexamers driving migration, is crucial for this process.

Purpose of the Study:

• To investigate the mechanism of RuvB translocation along DNA.
• To determine if DNA crosslinks affect the branch migration activity of the RuvAB complex.
• To challenge existing models of DNA helicase translocation.

Main Methods:

• Biochemical assays to study the RuvAB-Holliday junction complex.
• In vitro experiments using duplex DNA with site-directed interstrand psoralen crosslinks.
• Analysis of RuvB translocation in the presence of DNA crosslinks.

Main Results:

• The RuvB ring successfully translocated along duplex DNA containing an interstrand psoralen crosslink.
• The presence of the DNA crosslink did not inhibit the branch migration activity of the RuvAB complex.
• Holliday junction migration proceeded despite the structural impediment.

Conclusions:

• The findings challenge the base-by-base tracking model for RuvB translocation.
• Extensive DNA opening within the RuvB ring is likely not required for DNA translocation.
• RuvB may utilize a translocation mechanism that accommodates or bypasses DNA lesions like crosslinks.