Nat. Struct. Mol. Biol. 20, 274–281 (2013); published online 5 March 2013; corrected after print 5 June 2013

In the version of this article initially published, on p. 274, the sentence: “One key factor appears to be ZFP57 (also known as KAP1)...” should have read: “One key factor appears to be the ZFP57–KAP1 complex....” KAP1 is a ZFP57-binding partner. The error has been corrected in the HTML and PDF versions of the article.