Nat. Biotechnol. 20, 651 (2002).

Because of a proofreading error, Julian D. Watts' name was incorrect in the author affiliations.

The correct affiliations are as follows: Ruedi Aebersold is cofounder and Julian D. Watts is a senior research scientist, Institute for Systems Biology, 1441 North 34th Street, Seattle, WA 98103 (raebersold@systemsbiology.org). We regret the error.