Nature 437, 699–706 (2005)

In Fig. 1b of this Article, the x axis of the right-hand plot should be labelled 'α-Factor system output in each cell (CFP F.U. × 106)' and not 'ACT1 system output in each cell (CFP F.U. × 105)'. In addition, Supplementary Fig. S6 was incorrect as originally published and was replaced on 26 January 2006.