Scientists are just beginning to explore the idea that proteins inside bacterial cells may use the geometric shapes they encounter as localization cues (C&EN, Feb. 16, page 42). Now, Harvard University's Richard Losick and colleagues report evidence that the convex curvature of a spore as it forms at one end inside the rod-shaped bacterium Bacillus subtilis attracts and facilitates gathering of the membrane protein SpoVM (Science 2009, 323, 1354). Losick's group found that the protein preferred to collect on, and embed itself in, the convex outside surface of the forming spore, rather than on the concave membrane of the surrounding cell. Because an individual SpoVM molecule is small in comparison to the relatively gentle curvature of the inner cell, they suggest that several peptides may need to cluster together before becoming shape-sensitive. The group is also studying the possibility that some proteins may recognize concave curvature. "Simple geometry may play a larger role in the three-dimensional organization of cells than previously appreciated," Losick says.