Sci. STKE, 22 October 2002
DOI: 10.1126/stke.2002.155.pe44

The text of the figure from the Perspective by A. Ventura and P. Pelicci was unreadable. A new figure has been created. The online display has been corrected and a corrected PDF is available starting October 29, 2002.

The original, uncorrected PDF can be accessed from;2002/155/pe44/DC1/1.

Science Signaling. ISSN 1937-9145 (online), 1945-0877 (print). Pre-2008: Science's STKE. ISSN 1525-8882