Nat. Struct. Mol. Biol. 18, 423–431 (2011); published online 27 March 2011; corrected after print 6 April 2011
In the version of this article initially published, the acronym ENIGMA was spelled out incorrectly in the Acknowledgments section. 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.2038