consisting of VP90 were present in association with membranes as well as in
membrane-free fractions [ 53 ] . Based on these and related fi ndings [ 3 ] , a model was
proposed in which the viral progeny assemble in membranous structures, and then
dissociate from the membranes by an unknown mechanism; once in a membranefree
environment the assembled VP90 is then proteolytically cleaved at the
C-terminal end to yield viral particles containing VP70 (Fig. 2.6 ). This cleavage is
blocked by caspase inhibitors and induced by TRAIL (TNF-related apoptosis
ligand), suggesting an active role of caspases in the process [ 57 ] , although it is not
clear if VP90 processing occurs intracellularly or concomitantly with cell egress of
the virus . The involvement of caspases in this process is supported by the presence
of an acidic region in the C-terminal region of VP90, conserved