Nat. Biotechnol. 28, 503–510 (2010); published online 02 May 2010; corrected after print 9 July 2010

In the version of this article initially published, the fourth sentence in the Online Methods section “RNA extraction and library preparation,” that read in part “procedure that combines a random priming step with a shearing step8,9, 28 and results in fragments of 700 bp in size,” should have read, “procedure that combines fragmentation of mRNA to a peak size of 750 nucleotides by heating6 followed by random-primed reverse transcription8.” The error has been corrected in the HTML and PDF versions of the article.