Cover photograph (Copyright © 2007, American Society for Microbiology. All Rights Reserved.): Averaged atomic force microscopy image showing tridecameric c rings isolated from the ion-driven ATP synthase of the cyanobacterium Synechococcus elongatus SAG 89.79. The c13 rings are arranged in two orientations in the lipid bilayer, showing the cytoplasmic and periplasmic ring side. The wide end of the rings has an outer diameter of 6.6 nm. (See related article on page 5895.)