Cover photograph (Copyright © 2001, American Society for Microbiology. All rights reserved.): Replacement of tobacco mosaic virus (TMV) coat protein with green fluorescent protein (GFP) reveals viral movement on a tobacco leaf. The left half of the leaf was inoculated with TMV-U1C-GFP, a wild-type TMV strain. GFP expression indicates viral cell-to-cell movement. The right half was inoculated with UR-helC-GFP, a TMV strain in which substitutions in the replicase protein cause a deficiency in cell-to-cell movement. UR-helC-GFP did not result in fluorescent spots visible with the naked eye or without fluorescence microscopy. (See related article on page 8831.)