Nat. Chem. Biol. 6, 424–432 (2010); published online 9 May 2010; corrected after print 21 May 2010.

In the version of this article initially published, one of the cell lines used was erroneously given the mutant designation L444P in reference to Figure 6a, and another cell line did not include this designation in reference to Supplementary Figure 11 a,b. The errors in the main text have been corrected in the HTML and PDF versions of the article.