Structural basis for translocation by AddAB helicase–nuclease and its arrest at χ sites
A dual-function helicase–nuclease, typified by RecBCD in Escherichia coli , acts on free DNA ends during bacterial double-stranded break repair until it reaches a χ sequence at which it pauses before continuing with modified enzymatic properties; here several crystal structures of the related AddAB...
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| Veröffentlicht in: | Nature (London) Jg. 508; H. 7496; S. 416 - 419 |
|---|---|
| Hauptverfasser: | , , , , , |
| Format: | Journal Article |
| Sprache: | Englisch |
| Veröffentlicht: |
London
Nature Publishing Group UK
17.04.2014
Nature Publishing Group |
| Schlagworte: | |
| ISSN: | 0028-0836, 1476-4687, 1476-4687 |
| Online-Zugang: | Volltext |
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| Zusammenfassung: | A dual-function helicase–nuclease, typified by RecBCD in
Escherichia coli
, acts on free DNA ends during bacterial double-stranded break repair until it reaches a χ sequence at which it pauses before continuing with modified enzymatic properties; here several crystal structures of the related AddAB enzyme from
Bacillus subtilis
bound to χ-containing DNA are presented, offering insight into χ recognition and its effect on DNA translocation.
Taming a rampant nuclease
In bacterial double-stranded DNA break repair, the free ends are initially acted upon by a dual function helicase/nuclease, typified by the RecBCD enzyme of
Escherichia coli
. As RecBCD unwinds DNA, it eventually encounters a polar octameric sequence known as Chi (χ), which causes attenuation and a change in specificity of the nuclease activity. Dale Wigley and colleagues have now solved several structures of AddAB, a related enzyme from
Bacillus subtilis
, bound to χ-containing DNA. These structures offer insight into the translocation process, the recognition of χ, and the pausing that occurs when χ is recognized.
In bacterial cells, processing of double-stranded DNA breaks for repair by homologous recombination is dependent upon the recombination hotspot sequence χ (Chi)
1
,
2
and is catalysed by either an AddAB- or RecBCD-type helicase–nuclease (reviewed in refs
3
,
4
). These enzyme complexes unwind and digest the DNA duplex from the broken end until they encounter a χ sequence
5
, whereupon they produce a 3′ single-stranded DNA tail onto which they initiate loading of the RecA protein
6
. Consequently, regulation of the AddAB/RecBCD complex by χ is a key control point in DNA repair and other processes involving genetic recombination. Here we report crystal structures of
Bacillus subtilis
AddAB in complex with different χ-containing DNA substrates either with or without a non-hydrolysable ATP analogue. Comparison of these structures suggests a mechanism for DNA translocation and unwinding, suggests how the enzyme binds specifically to χ sequences, and explains how χ recognition leads to the arrest of AddAB (and RecBCD) translocation that is observed in single-molecule experiments
7
,
8
,
9
. |
|---|---|
| Bibliographie: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 Present address: CRT Discovery Laboratories, Department of Biological Sciences, Birkbeck, University of London, London, U.K. Contributions: W.W.K. & D.B.W designed the experiments. W.W.K., X.F., M.W and N.B.C performed the experiments. W.W.K., M.W., M.S.D. and D.B.W. analysed the data and prepared the manuscript. |
| ISSN: | 0028-0836 1476-4687 1476-4687 |
| DOI: | 10.1038/nature13037 |