Nat. Chem. Biol. 9, 475–484 (2013); published online 18 July 2013; corrected after print 19 December 2013

In the version of this Review Article initially published, a double bond was missing from the chemical structure of the cyclooctene on the left side of the reaction arrow in Figure 1e. The chemical structure has been corrected in the HTML and PDF versions of the article.