Nat. Chem. Biol. 10, 632–639 (2014); published online 22 June 2014; corrected after print 29 July 2014 and 14 August 2014

In the version of this article initially published, a black bar was erroneously placed in the scrambled shRNA column in Figure 3g. The error has been corrected for the PDF and HTML versions of the article.