Cover photograph (Copyright © 2003, American Society for Microbiology. All Rights Reserved.): Model for the probable three-dimensional arrangement of helices in proteins belonging to the major facilitator superfamily, derived from combining cryoelectron microscopic studies of two-dimensional crystals of the oxalate transporter OxlT with bioinformatic analyses of related proteins in the family. The helices are shown as idealized straight cylinders, and the regions connecting proposed neighboring helices are shown as unstructured loops. (See related article on page 1712.)