Nat. Biotechnol. 24, 537–544 (2006)

In the print version of this article and the version originally published online, reference 5 was mistakenly included on page 537, column 2, lines 3, 10 and reference 1 on line 17, and the line “Ouzounis8 and the Prospectr scores from Euan Adie9” was repeated in the acknowledgments on page 544.