Figure 1.

Molecular determinants regulating genome bundling and genome packaging. After accumulation close to the microtubule-organizing center (MTOC), viral ribonucleoprotein (vRNP) complexes are transported as vRNP sub-bundles on Rab11 recycling vesicles (genome bundling) towards the plasma membrane to be incorporated as a complex of eight different vRNPs into budding virions (genome packaging). ‘Genome packaging’ (upper panel) is regulated by packaging sequences (indicated in red). The molecular elements required for ‘genome bundling’ (lower panel) are currently unknown and could involve either (a) packaging sequences (red) or (b) yet unknown bundling determinants (green) including secondary RNA structures or host factors.