Nat. Chem. Biol. 7, 566–574 (2011); published online 10 July 2011; corrected after print 26 July 2011

In the version of this article initially published, in paragraph 3 of the results section entitled “UNC0638 is a potent and substrate-competitive inhibitor,” the units for the association rate (ka) were listed incorrectly. The correct unit is 1/Ms. This error has been corrected in the HTML and PDF versions of the article.