Nat. Chem. Biol. 10, 632–639 (2014); published online 22 June 2014; corrected after print 29 July 2014

In the version of this article initially published, Julia TCW's name was misspelled as Julia T C W. In addition, her initials in the author contribution statement should have read J.T. instead of J.T.C.W. The error has been corrected in the HTML and PDF versions of the article.