Animal cell invasion by a large nonenveloped virus: Reovirus delivers the goods

Molecular mechanisms by which nonenveloped animal viruses penetrate a cellular membrane to invade the host cytoplasm remain less well characterized than those used by enveloped viruses. Mammalian reoviruses are useful agents for addressing this problem, especially in light of recent crystal structure determinations for the viral proteins and development of a new genetic tool with which to dissect the viral determinants of cell invasion. The roles of penetration protein μ1 and its protector protein σ3 are beginning to come into focus.