Ono and Ono, Vol. 156, No. 6, March 18, 2002. Pages 1065–1076.

On page 1074, the affiliations supplied for Drs. M. Hresko and A. Fire were incorrect. M. Hresko's correct institutional affiliation is Washington University School of Medicine, St. Louis, MO; A. Fire's correct institutional affiliation is Carnegie Institution of Washington, Baltimore, MD.