Nat. Chem. Biol. 13, 551–557 (2017); published online 20 March 2017; corrected after print 4 April 2017

In the version of this article initially published, the compound structure immediately upstream of DPO in the biosynthetic scheme in Figure 4e was redrawn incorrectly during production. The structure was missing a methyl group. The error has been corrected in the HTML and PDF versions of the article.