A fundamental feature of development in the spore-forming bacterium Bacillus subtilis is the switch from medial to asymmetric division. The switch is brought about by a change in the location of the cytokinetic Z ring, which is composed of the tubulin-like protein FtsZ, from the cell middle to the poles during sporulation. We report that the medial Z ring is replaced by a spiral-like filament of FtsZ that grows along the long axis of the cell. We propose that the filament mediates the switch by redeploying FtsZ to the poles. Spiral formation and the switch to polar Z rings are largely caused by a sporulation-specific increase in transcription of the gene for FtsZ and activation of the gene for the FtsZ-associated protein SpoIIE.
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We thank D. Rudner and E. Gonzalez for valuable discussions, M. Fujita, K. Carniol, and D. Smith for technical advice, and J. Kemp and P. Levin for strains. We thank L. Shapiro, W. Margolin, P. Stragier, K. Pogliano, P. Levin, and members of the Losick laboratory for helpful comments on the manuscript. We also thank R. Helmiss for the computer graphics. S.B.-Y. was a Fulbright postdoctoral scholar and is a postdoctoral fellow of the Human Frontier Science Program. This work was supported by National Institutes of Health grant GM18568 to R.L.