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Cover  The structure of the extracted bacterial flagellar motor was described in a seminal paper by Dennis Thomas, David Morgan, and David DeRosier (1999, "Rotational Symmetry of the C-ring and a Mechanism for the Flagellar Rotary Motor." Proc. Natl. Acad. Sci. USA 96, 10134-10139). The left panel is an image of the flagellar basal body obtained by averaging electron micrographs of many individual flagellar basal structures. At the bottom is the cytoplasmic C ring, which extends from the M ring, the portion of the structure that resides within the cytoplasmic membrane (IM). Above them are the P and L rings, which are located in the periplasm and outer membrane (OM), respectively. The L and P rings are threaded on an axel-like rod, which traverses the surface layers of Gram-negative bacteria. The right panel is a contour plot of the density of the averaged image. Three of the five proteins essential for the torque generation are located in the C and M rings, and a mechanism for torque generation was proposed that is based on the symmetry mismatch between these two rings. Professor Lucy Shapiro.