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PDBsum entry 6pij
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RNA binding protein/RNA/DNA
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PDB id
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6pij
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Contents |
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351 a.a.
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310 a.a.
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511 a.a.
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197 a.a.
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358 a.a.
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369 a.a.
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References listed in PDB file
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Key reference
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Title
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Structural basis of DNA targeting by a transposon-Encoded crispr-Cas system.
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Authors
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T.S.Halpin-Healy,
S.E.Klompe,
S.H.Sternberg,
I.S.Fernández.
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Ref.
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Nature, 2020,
577,
271-274.
[DOI no: ]
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PubMed id
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Note: In the PDB file this reference is
annotated as "TO BE PUBLISHED". The citation details given above have
been manually determined.
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Abstract
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Bacteria use adaptive immune systems encoded by CRISPR and Cas genes to maintain
genomic integrity when challenged by pathogens and mobile genetic
elements1-3. Type I CRISPR-Cas systems typically target foreign DNA
for degradation via joint action of the ribonucleoprotein complex Cascade and
the helicase-nuclease Cas34,5, but nuclease-deficient type I systems
lacking Cas3 have been repurposed for RNA-guided transposition by bacterial
Tn7-like transposons6,7. How CRISPR- and transposon-associated
machineries collaborate during DNA targeting and insertion remains unknown. Here
we describe structures of a TniQ-Cascade complex encoded by the Vibrio cholerae
Tn6677 transposon using cryo-electron microscopy, revealing the mechanistic
basis of this functional coupling. The cryo-electron microscopy maps enabled de
novo modelling and refinement of the transposition protein TniQ, which binds to
the Cascade complex as a dimer in a head-to-tail configuration, at the interface
formed by Cas6 and Cas7 near the 3' end of the CRISPR RNA (crRNA). The natural
Cas8-Cas5 fusion protein binds the 5' crRNA handle and contacts the TniQ dimer
via a flexible insertion domain. A target DNA-bound structure reveals critical
interactions necessary for protospacer-adjacent motif recognition and R-loop
formation. This work lays the foundation for a structural understanding of how
DNA targeting by TniQ-Cascade leads to downstream recruitment of additional
transposase proteins, and will guide protein engineering efforts to leverage
this system for programmable DNA insertions in genome-engineering applications.
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