Received 29 October 2008; accepted 19 February 2009; published online 17 May 2009; corrected after print 19 May 2009

In the version of this article initially published, the Myc–Ub label in Figure 3c was incorret. Arrowheads were missing in Fig. 5d and 5e. A plus (+) was misplaced from the curve in Fig. 7c. The correct versions of these figures are shown below. These errors have been corrected in the HTML and PDF versions of the article.