Nature Cell Biol. 12, 111–118 (2010); published online 24 January 2010; corrected after print, 27 January 2010

In the version of this Article initially published, Fig. 4d was incorrectly labelled “−Inositol” and “+Inositol”. They should actually be labelled “no GRS” and “+GRS”. The correct version of this figure is shown below. This error has been corrected in the HTML and PDF version of the article.