FIG. 7.

Signals regulating trafficking of the MVM virus across the nuclear membrane. Cytoplasmic entry events are as follows: cleavage of 2Nt and externalization of the NLS contained in the VP1 N terminus contribute to the docking of the incoming virus to the NPC. Nuclear export events are as follows: the viral structural proteins translocated to the nucleus by import sequences (Fig. 1) assemble first into empty capsids that likely act as intermediates of viral maturation. Genome encapsidation triggers the externalization of 2Nt of some VP2 subunits outside the capsid shell, driving the active export of mature virus. In transformed cells, a high level of capsid phosphorylation endows 2Nt with NES activity (route 1), whereas in normal fibroblasts the lower 2Nt phosphorylation restricts virus nuclear export to a CRM1-dependent mechanism requiring the infection process (route 2).