Nat. Struct. Mol. Biol. 18, 708–714 (2011); published online 22 May 2011; corrected after print 3 June 2011.
In the version of this article initially published, the affiliation for authors at the Department of Molecular and Cellular Biology, Centro Nacional de Biotecnología, Madrid, Spain, was incomplete. The full affiliation is “Department of Molecular and Cellular Biology, Centro Nacional de Biotecnología, CSIC, Madrid, Spain.” The error has been corrected in the HTML and PDF versions of the article.
The online version of the original article can be found at 10.1038/nsmb.2059