Nat. Cell Biol. 12, 87–93 (2010); published online 13 December 2009; corrected after print 16 May 2011

In the version of this article initially published online and in print, an incorrect link was provided by Nature Cell Biology in the Competing Financial Interests. The Competing Financial Interests should have included the following statement that was correctly submitted by the authors prior to publication: The University of California, San Diego, has submitted a patent form on behalf of J.I.S., M.I-N., J.M.K., H.H. and A.B.D. on aspects of the findings. This error has been corrected in both the HTML and PDF versions of the article.