Nat. Methods 4, 13–17 (2007); published online 28 December 2006; corrected after print 18 January 2007.

In the version of the article originally published, Manfred Koegl's name was misspelled. Additionally, Zoltán Konthur's affiliation was incorrect; it should be Max Planck Institute for Molecular Genetics, 14195 Berlin, Germany. These errors have been corrected in the HTML and PDF versions of the article.