Nature 407 , 1015 - 1017 (2000).

The address of the author Emma J. Kidd was cited incorrectly. Her affiliation should have been given as the Glaxo Institute of Applied Pharmacology, Department of Pharmacology. University of Cambridge, Tennis Court Road, Cambridge CB2 1QJ, UK, which was where her work was carried out. The Welsh School of Pharmacy, Cardiff University, Cardiff CF1 3XF, UK, which was cited as her affiliation in this paper, is her present address.