Previously, we reported that virion uncoating mediated by Cat S does not require acidic pH [3] . These results were consistent with the acid-independence of Cat S activity [37] . Together, the results in Fig. 2 and Fig. 4 reveal that, like Cat S, NE-mediates infection in an acid-independent manner. This finding thus provides further support for a model in which the requirement for acidic pH during reovirus infection of some cell types reflects the requirement for acid-dependent protease activity in those cells rather than some other requisite acid-dependent aspect of cell entry. The small effect of Baf and NH 4 Cl on E64-resistant reovirus growth (Fig. 2 ) may reflect the participation of one or more acid-dependent proteases (such as Cat D) in the activation of NE.