Nature 386, 366–373 (1997)

We inadvertently omitted to acknowledge D. Ish-Horowitz for the Ser-2 clone and for supporting D.H. (through funds awarded by the ICRF and HFSPO), and T. Vogt, S. H. Johnston, C. Rauskolb, E. Wieschaus, K. Irvine, S. Egan, Y. Rao, Y. Wang and P. Leder for sharing unpublished results.