Nat. Struct. Mol. Biol. 23, 172–179 (2016); published online 18 January 2016; corrected after print 8 December 2016

In the version of this article initially published, the x-axis of the bottom left graph in Figure 4d was incorrectly labeled as showing time in minutes; in actuality, the data in the graph align with the conditions indicated for the blot images above. The error has been corrected in the HTML and PDF versions of the article.