Figure 3.

Transport of an RNP from virion to nucleus. Schematic showing viral entry and the passage of RNPs to the nucleus. Spherical (left) and filamentous (right) virions bind to sialic-acid bearing receptors on the cells surface and are imported by clathrin-mediated endocytosis (left) or macropinocytosis (right). The increasing acidity of their environment (indicated by yellow shading) results in conformational changes in M2, causing filaments to fragment (right). Changes in pH are transmitted through M2 to the virion interior, where they cause M1 to dissociate from RNPs. The increasing acidity also causes conformational changes in HA, which inserts into the endosomal membrane and mediates membrane fusion, expelling a complex of uncoated RNPs into the cytoplasm. The complex of RNPs interacts with the classical nuclear import pathway and dissociates in the nucleus (bottom). See text for details.