Cover photograph (Copyright © 2001, American Society for Microbiology. All rights reserved.): The rotavirus spike structure is stabilized and ordered by trypsin treatment, providing a mechanism for enhanced infectivity. VP4 spikes (in red) are well ordered on virus grown in the presence of trypsin (upper left) but are disordered and not detectable by cryoelectron-microscopic reconstructions of virus grown in the absence of trypsin (upper right). The spike structure does not change following additional trypsin treatment of rotavirus grown in the presence of trypsin (lower left). VP4 spikes gain some, but not complete, order and become detectable in the reconstruction of rotavirus (lower right) grown in the absence of trypsin and subsequently treated with trypsin. (See related article on page 6052.)