Nat. Chem. Biol. 4, 287–289 (2008); published online 6 April 2008; corrected after print 1 May 2008

In the version of this article initially published, parentheses were missing around covalently attached domains in fusion proteins. Also, in the first two lines of the left column of page 288, “hTERT-YFP” should have read “YFP-hTERT” for consistency with the rest of the manuscript. The errors have been corrected in the HTML and PDF versions of the article.