Cover photograph (Copyright © 2006, American Society for Microbiology. All Rights Reserved.): Internalization of mammalian reovirus into β1 integrin-deficient mouse embryonic stem cells. Cells were adsorbed with reovirus at 4°C and then warmed to 37°C to allow virus internalization. Cells were fixed at 20 min postadsorption, stained for reovirus (green), actin (red), and DNA (blue), and imaged using confocal immunofluorescence microscopy. The majority of reovirus particles are localized around the cell periphery, rather than in the perinuclear space as observed following infection of wild-type cells, indicating that reovirus internalization is less efficient in the absence of β1 integrin. (See related article on page 2760.)