Nat. Chem. Biol. 12 i–iii (2016); published online 19 January 2016; corrected after print 11 February 2016

In the version of this caption initially published, the cover artwork was credited to Erin Dewalt, based on imagery from the author, rather than stating that it was created by Michael B. Battles and the design was by Erin Dewalt. The error has been corrected in the HTML and PDF versions of the caption.