Cover photograph (Copyright © 2000, American Society for Microbiology. All rights reserved.): The conversion of poliovirus 160S virions (top) into 135S particles (bottom), an early event in cell entry, is accompanied by tectonic movements of the core domains (right) of capsid proteins VP1 (cyan), VP2 (yellow), and VP3 (red). These movements were modeled by adjusting the core domainsknown from crystallography of the virionto fit the cryoelectron microscopy reconstruction of the 135S particle (bottom left). A few subunits are colored on the reconstructions (left). Arrows indicate some of the observed shifts. Micrographs of the respective particles are in the background. (See related article on page 1342.)