Cover photograph (Copyright © 2006, American Society for Microbiology. All Rights Reserved.): Bacterial flagellum extracted from a filament-negative Salmonella strain with a clockwise-locked rotary motor. The three-dimensional reconstructions, some still in progress, were generated from electron cryomicrographs of frozen hydrated samples. Starting from the top: in blue, axial/helical components, including cap, hook-filament junction, hook (or universal joint), and rod (or drive shaft); in purple, L and P rings (or bushing); in yellow, proposed location of FliF, a transmembrane protein that couples the motor to the drive shaft; in red, proposed location of FliG, one of the motor/switch proteins; in blue, proposed location of FliM and FliN, two other motor/switch proteins. (See related article on page 7039.)