Nat. Cell Biol. 12, 507–512 (2010); published online 18 April 2010; corrected after print, 9 July 2010

In the version of this letter initially published online and in print, Fig. 4e–j were incorrectly labelled: ISC and ΔISC should be ICI and ΔICI, respectively. The correct labelling is shown below. These errors have been corrected in both the HTML and PDF versions of the letter.