FIG. 8.

Model for the assembly of VLPs (A), virions (B), and tubules (C). We hypothesized that the VP3 protein has two different conformations in thermodynamic equilibrium: a relaxed state (pink) and an activated one (red). Only the activated VP3 is supposed to self-assemble. Quaternary interactions involving VP3 and GFP (A) or VP3 and genomic RNA-VP1 (B) shift the equilibrium toward the activated form, favoring the spontaneous assembly of VP3 subviral particles. The proteolytic maturation of pVP2 into VP2 requires interaction with assembled VP3. When the equilibrium is not shifted, the activated VP3 forms nuclei only for the polymerization of pVP2 into tubules (C). The existence of the VP3 nuclei for the polymerization of pVP2 has been proposed by Martinez-Torrecuadrada et al. (17) and agrees with the fact that pVP2 alone self-assembles not into tubules but into isometric particles.