RuvABC

'''RuvABC''' is a complex of three proteins that mediate branch migration and resolve the Holliday junction created during homologous recombination in bacteria.<ref name="Wyatt2014">{{cite journal |last1=Wyatt |first1=Hayley D. M. |last2=West |first2=Stephen C. |title=Holliday Junction Resolvases |journal=Cold Spring Harbor Perspectives in Biology |date=1 September 2014 |volume=6 |issue=9 |article-number=a023192 |doi=10.1101/cshperspect.a023192|pmid=25183833 |pmc=4142969 }}</ref> As such, RuvABC is critical to bacterial DNA repair.

thumb|320px|right|RuvA-RuvB complex heteromer, Thermus thermophilus 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.<ref name="Henkin2020" /> 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 homologous recombination. In ''Escherichia coli'', DNA replication forks stall at least once per cell cycle, so that DNA replication must be restarted if the cell is to survive.<ref name = Bianco2021>{{cite journal |last1=Bianco |first1=Piero R |last2=Lu |first2=Yue |title=Single-molecule insight into stalled replication fork rescue in ''Escherichia coli'' |journal=Nucleic Acids Research |date=7 May 2021 |volume=49 |issue=8 |pages=4220–4238 |doi=10.1093/nar/gkab142 |pmid=33744948 |pmc=8096234}}</ref> 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.<ref name = Bianco2021/> The resolution of Holliday junctions that accumulate following replication on damaged DNA templates in ''E. coli'' requires the RuvABC complex.<ref>{{cite journal |last1=Donaldson |first1=Janet R. |last2=Courcelle |first2=Charmain T. |last3=Courcelle |first3=Justin |title=RuvABC Is Required to Resolve Holliday Junctions That Accumulate following Replication on Damaged Templates in ''Escherichia coli'' |journal=Journal of Biological Chemistry |date=September 2006 |volume=281 |issue=39 |pages=28811–28821 |doi=10.1074/jbc.M603933200 |pmid=16895921 |doi-access=free}}</ref> ===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 and EM data.<ref name="Eggleston1997">{{cite journal |last1=Eggleston |first1=Angela K |last2=Mitchell |first2=Alison H |last3=West |first3=Stephen C |date=May 1997 |title=In Vitro Reconstitution of the Late Steps of Genetic Recombination in E. coli |journal=Cell |volume=89 |issue=4 |pages=607–617 |doi=10.1016/S0092-8674(00)80242-1|pmid=9160752 |doi-access=free }}</ref> RuvA forms a tetramer that binds to the Holliday junction and forces it into a planar configuration.<ref name="Henkin2020" /><ref name="Yamada2004" /> In some cases, a second tetramer binds to the opposite face of the DNA, forming a shell around the junction.<ref name="Henkin2020" /><ref name="Yamada2004" /> The RuvA tetramer has acidic pins near its center that facilitate unwinding and contribute to substrate specificity.<ref name="Wyatt2014" /><ref name="Yamada2004" />

===RuvB=== '''RuvB''' is a DNA-dependent ATPase that forms a hexameric ring around the arms of the Holliday junction.<ref name="Henkin2020" /><ref name="Eggleston1997" /> 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.<ref name="Wyatt2014" />

===RuvC=== '''RuvC''' is the resolvase, which cleaves the Holliday junction. RuvC binds to Holliday junctions as a homodimer.<ref name="Wyatt2014" /> As a homodimer, there are two active endonuclease sites, each of which can form a double-strand break.<ref name="Henkin2020">{{cite book |last1=Henkin |first1=Tina M. |last2=Peters |first2=Joseph E. |title=Molecular Genetics of Bacteria |date=2020 |publisher=American Society for Microbiology |isbn=978-1-68367-357-6 |pages=371–373 |edition=Fifth |chapter=Molecular Mechanisms of Homologous Recombination}}</ref> RuvC can be bound to the complex in either orientation, therefore resolving Holliday junctions in either a horizontal or vertical manner.<ref name="Eggleston1997" /> There are multiple theories as to how RuvC is able to access the branch migration complex.<ref name="Yamada2004">{{cite journal |last1=Yamada |first1=Kazuhiro |last2=Ariyoshi |first2=Mariko |last3=Morikawa |first3=Kosuke |title=Three-dimensional structural views of branch migration and resolution in DNA homologous recombination |journal=Current Opinion in Structural Biology |date=April 2004 |volume=14 |issue=2 |pages=130–137 |doi=10.1016/j.sbi.2004.03.005 |pmid=15093826 }}</ref> 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.<ref name="Henkin2020" />

==See also== *RecBCD

== References == <references />

==Further reading== * {{cite journal |last1=West |first1=Stephen C. |title=Molecular views of recombination proteins and their control |journal=Nature Reviews Molecular Cell Biology |date=June 2003 |volume=4 |issue=6 |pages=435–445 |doi=10.1038/nrm1127 |pmid=12778123 |s2cid=28474965 }} * {{cite journal |last1=Kowalczykowski |first1=Stephen C |title=Initiation of genetic recombination and recombination-dependent replication |journal=Trends in Biochemical Sciences |date=April 2000 |volume=25 |issue=4 |pages=156–165 |doi=10.1016/S0968-0004(00)01569-3 |pmid=10754547 }}

==External links== * {{MeshName|Holliday+Junction+Resolvases}}

Category:Protein complexes Category:Bacterial enzymes