ABSTRACT Oligomeric complexes of Trax and Translin proteins, known as C3POs, participate in several eukaryotic nucleic acid metabolism pathways, including RNA interference and tRNA

processing. In RNA interference in humans and _Drosophila_, C3PO activates the RNA-induced silencing complex (RISC) by removing the passenger strand of the small interfering RNA precursor

duplex, using nuclease activity present in Trax. How C3POs engage with nucleic acid substrates is unknown. Here we identify a single protein from _Archaeoglobus fulgidus_ that assembles into

an octamer highly similar to human C3PO. The structure in complex with duplex RNA reveals that the octamer entirely encapsulates a single 13-base-pair RNA duplex inside a large inner

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Source, UK for help with data collection. This work was funded by a UK Medical Research Council Career Development Award to J.S.P. (grant no. G0600097). The pTwo-E vector was a gift from A.

Oliver, University of Sussex, Brighton, UK. AUTHOR INFORMATION AUTHORS AND AFFILIATIONS * Department of Biochemistry, University of Oxford, Oxford, UK Eneida A Parizotto, Edward D Lowe 

& James S Parker Authors * Eneida A Parizotto View author publications You can also search for this author inPubMed Google Scholar * Edward D Lowe View author publications You can also

search for this author inPubMed Google Scholar * James S Parker View author publications You can also search for this author inPubMed Google Scholar CONTRIBUTIONS E.A.P. produced and

purified the proteins, grew the crystals and performed the biochemical assays. E.D.L. provided advice, maintained facilities and assisted with X-ray data collection. J.S.P. collected X-ray

data, determined the structures and wrote the manuscript. CORRESPONDING AUTHOR Correspondence to James S Parker. ETHICS DECLARATIONS COMPETING INTERESTS The authors declare no competing

financial interests. SUPPLEMENTARY INFORMATION SUPPLEMENTARY TEXT AND FIGURES Supplementary Figures 1–6 (PDF 3102 kb) RIGHTS AND PERMISSIONS Reprints and permissions ABOUT THIS ARTICLE CITE

THIS ARTICLE Parizotto, E., Lowe, E. & Parker, J. Structural basis for duplex RNA recognition and cleavage by _Archaeoglobus fulgidus_ C3PO. _Nat Struct Mol Biol_ 20, 380–386 (2013).

https://doi.org/10.1038/nsmb.2487 Download citation * Received: 20 September 2012 * Accepted: 10 December 2012 * Published: 27 January 2013 * Issue Date: March 2013 * DOI:

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