Cover photograph (Copyright © 2001, American Society for Microbiology. All rights reserved.): Ribbon diagram of fibroblast growth factor 4 (FGF4). The core domain of FGF4 adopts a -trefoil fold that consists of three four-strand  sheets. The view is chosen to best illustrate the symmetry of the -trefoil motif. The FGF4 structure assisted in the identification of several receptor and heparin binding sites in FGF4. (See related article on page 5946.)