Nat. Biotechnol. 35, 475–480 (2017); published online 10 April 2017; corrected after print 6 July 2017

In the version of this article initially published, in the HTML only, Daesik Kim should have been the second corresponding author rather than Seuk-Min Ryu. In Figure 4b, in all versions, the bar graphs were misaligned with the specificity ratios, so that the first row of bar graphs were above the specificity ratios, rather than aligned with 3.5, 1.0, etc. The errors have been corrected in the HTML and PDF versions of the article.