Nat. Biotechnol. 34, 345–352 (2016); published online 29 January 2016; corrected after print 18 April 2016

In the version of this article initially published, one author, Adam C. Graham, his affiliation, and his contribution were omitted. In addition, two acknowledgments, to W. Salmon and J. Wyckoff, were omitted. The errors have been corrected in the HTML and PDF versions of the article.