Nat. Cell Biol. 16, 55–65 (2014); published online 8 December 2013; corrected after print 16 December 2013

In the version of this Article originally published, the 'Anti-FLAG' label at the top-right of the right panel in Fig. 1b should have read 'Anti-GFP'. This error has now been corrected in the online versions of the Article.