Nat. Methods 10, 623–629 (2013); published online 19 May 2013; corrected after 2 December 2013

In the version of this article initially published, in the Online Methods “RNase H libraries” section, the sentence beginning with “We added 5 μl preheated RNase H....” should have read “We added 5 μl preheated RNase H reaction mix that contains 10 U of Hybridase Thermostable RNase H (Epicentre), 0.5 μmol Tris-HCl, pH 7.5, 1 μmol NaCl and 0.2 μmol MgCl2 to the RNA and DNA oligo mix, incubated this mixture at 45 °C for 30 min and then placed it on ice.” The errors have been corrected in the HTML and PDF versions of this article.