Nonequilibrium self-assembly dynamics of icosahedral viral capsids packaging genome or polyelectrolyte

The survival of viruses partly relies on their ability to self-assemble inside host cells. Although coarse-grained simulations have identified different pathways leading to assembled virions from their components, experimental evidence is severely lacking. Here, we use timeresolved small-angle X-ray scattering to uncover the nonequilibrium self-assembly dynamics of icosahedral viral capsids packaging their full RNA genome. We reveal the formation of amorphous complexes via an en masse pathway and their relaxation into virions via a synchronous pathway. The binding energy of capsid subunits on the genome is moderate (similar to 7k(B)T(o), with k(B) the Boltzmann constant and T-o = 298 K, the room temperature), while the energy barrier separating the complexes and the virions is high (similar to 20k(B)T(o)). A synthetic polyelectrolyte can lower this barrier so that filled capsids are formed in conditions where virions cannot build up. We propose a representation of the dynamics on a free energy landscape.