Nat. Med. 17, 454–460 (2012); published online 3 April 2011; corrected after print 5 October 2012

In the version of this article initially published, the authors inadvertently used α-tubulin normalization data in the western blots shown in Figure 4b and Figure 4e from separate experiments used to generate the other bands shown. The error did not affect the main conclusions of the paper. Nonetheless, to verify the data, the authors have repeated the experiments, and the data from one such experiment are now included for both these figure panels. The authors regret the occurrence and apologize for it. The error has been corrected in the HTML and PDF versions of the article.