RuvABC is a complex of three

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

s that mediate branch migration and resolve the Holliday junction created during

homologous recombination Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in Cell (biology), cellular organi ...

in bacteria. As such, RuvABC is critical to bacterial

DNA repair DNA repair is a collection of processes by which a cell (biology), cell identifies and corrects damage to the DNA molecules that encode its genome. A weakened capacity for DNA repair is a risk factor for the development of cancer. DNA is cons ...

. RuvA and RuvB bind to the four strand DNA structure formed in the Holliday junction intermediate, and migrate the strands through each other, using a putative spooling mechanism. The RuvAB complex can carry out DNA helicase activity, which helps unwind the duplex DNA. The binding of the RuvC protein to the RuvAB complex is thought to cleave the DNA strands, thereby resolving the Holliday junction.

Protein complex

The RuvABC is a complex of three proteins that resolve the Holliday junction formed during bacterial

. In ''

Escherichia coli ''Escherichia coli'' ( )Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. is a gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Escherichia'' that is commonly fo ...

'',

DNA replication In molecular biology, DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. DNA replication occurs in all life, living organisms, acting as the most essential part of heredity, biolog ...

forks stall at least once per cell cycle, so that DNA replication must be restarted if the cell is to survive. Replication restart is a multi-step process in ''E. coli'' that requires the sequential action of several proteins. When the progress of the replication fork is impeded, the single-stranded binding protein and RecG helicase along with the RuvABC complex are required for rescue. The resolution of Holliday junctions that accumulate following replication on damaged DNA templates in ''E. coli'' requires the RuvABC complex.

RuvA

RuvA is a DNA-binding protein that binds Holliday junctions with high affinity. The structure of the complex has been variously elucidated through

X-ray crystallography X-ray crystallography is the experimental science of determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to Diffraction, diffract in specific directions. By measuring th ...

and EM data. RuvA forms a tetramer that binds to the Holliday junction and forces it into a planar configuration. In some cases, a second tetramer binds to the opposite face of the DNA, forming a shell around the junction. The RuvA tetramer has acidic pins near its center that facilitate unwinding and contribute to substrate specificity.

RuvB

RuvB is a DNA-dependent

ATPase ATPases (, Adenosine 5'-TriPhosphatase, adenylpyrophosphatase, ATP monophosphatase, triphosphatase, ATP hydrolase, adenosine triphosphatase) are a class of enzymes that catalyze the decomposition of ATP into ADP and a free phosphate ion or ...

that forms a hexameric ring around the arms of the Holliday junction. RuvB is thought to pump the DNA through RuvA using the energy generated by the hydrolysis of ATP. This converts the homoduplex DNA into heteroduplex.

RuvC

RuvC is the resolvase, which cleaves the Holliday junction. RuvC binds to Holliday junctions as a homodimer. As a homodimer, there are two active

endonuclease In molecular biology, endonucleases are enzymes that cleave the phosphodiester bond within a polynucleotide chain (namely DNA or RNA). Some, such as deoxyribonuclease I, cut DNA relatively nonspecifically (with regard to sequence), while man ...

sites, each of which can form a double-strand break. RuvC can be bound to the complex in either orientation, therefore resolving Holliday junctions in either a horizontal or vertical manner. There are multiple theories as to how RuvC is able to access the branch migration complex. One theory is that a RuvA tetramer binds only to one side of the DNA, leaving an exposed face for RuvC to bind to. An alternative theory is that RuvA does not maintain the shell like structure it initially forms around the junction, but rather opens up to allow RuvC to access the DNA.

References

External links

* {{MeshName, Holliday+Junction+Resolvases Protein complexes Bacterial enzymes