Bibliographical noteFunding Information:
We thank Janine Maddock for providing the electron micrograph of C. crescentus shown in Fig. 1, and Yves Brun and Bert Ely for communicating unpublished data. We also thank Keith Chater, Alan Grossman, Dale Kaiser, Roberto Kolter, Sharon Long, and Dan Wall for critical reading of the manuscript, and members of the Shapiro laboratory for helpful discussions. R.C.R. was supported by American Cancer Society postdoctoral fellowship PF-3831, and C.D.M. was supported by American Cancer Society postdoctoral fellowship PF-3941. Work in the Shapiro laboratory was supported by Grants GM32506 and GM51426 from the National Institutes of Health.