Nat. Biotechnol. 33, 538–542 (2015); published online 23 March 2015; corrected online 16 April 2015

In the version of this article initially published online, the received date of the paper was given as 17 October 2014; the correct date is 11 July 2014. On p.4, left column, second paragraph, 1 μM Scr7 should have been 1 mM Scr7; in Online Methods, second paragraph, Cas9 mRNA, sgRNA and template oligos were erroneously given in ng/ml rather than ng/μl. A technique was misidentified as ChIP; in all cases it should be “chip.” The possibility of using Scr7 as a means of enhancing homology-directed repair was recently also mentioned in a review article that was published while our manuscript was under review. A reference to this article has been added to the manuscript. Finally, the P values in Table 1 for Kell and Lgkc were reversed and should be *P < 0.05 (Igkc), ***P < 0.005 (Kell) and not *P < 0.05 (Kell), ***P < 0.005 (Igkc). The errors have been corrected for the print, PDF and HTML versions of this article.