Nat. Biotechnol. 35, 725–731 (2017); published online 8 August 2017; corrected after print 29 November 2017; corrected after print 7 December 2017
In the version of this article initially published, the following acknowledgment was omitted: A.L. was supported by the Russian Science Foundation (grant number 14-50-00069). The error has been corrected in the HTML and PDF versions of the article.