Nature Cell Biol. 9, 445–452 (2007); published online 11 March 2007; corrected after print 16 October 2008

In the version of this article initially published, the third and fifth histogram columns in the right panel of Fig. 2a were incorrectly labelled. The third column should have been siUCP3 and the fifth should have been siUPC2.

These errors have been corrected in the HTML and PDF versions of the article.