Nat. Biotechnol. 31, 961–964 (2013); doi:10.1038/nbt.2729; published online 31 October 2013; corrected after print 26 November 2013

In the version of this article initially published, the Twitter contact was listed as @PureTechV. The correct contact is @PureTechH. The error has been corrected in the HTML and PDF versions of the article.