Nat. Chem. Biol. 5, 462–464 (2009); published online 17 May 2009; corrected after print 18 August 2009

In the version of this article initially published, the fourth author's last name is misspelled. The author's name should read “Yazmid Reyes-Dominguez.” The error has been corrected in the HTML and PDF versions of the article.