Viral assembly is an intriguing topic of biophysics that can be studied using concepts of soft matter physics. Although huge efforts have been made to synthesize hybrid or non-hybrid supramolecular assemblies with viral proteins, the fundamental mechanisms of self-assembly are yet poorly understood. In particular, the kinetic pathway in which the proteins interact with the genome to form highly symmetrical monodisperse architectures are not completely solved.In the first part of this thesis, the Time-Resolved Small-Angle X-Ray Scattering (TR-SAXS) technique is used to probe the kinetics of both self-assembly and disassembly of empty capsids built up from the proteins of the Cowpea Chlorotic Mottle Virus (CCMV). Chemical kinetics models coupled with concepts of SAXS theory are devised in order to extract information about the nature of the reaction intermediates, their structure and their typical lifetime. The encapsulation of ssRNA with CCMV capsid proteins is also examined in this thesis. At neutral pH where the capsid proteins do not spontaneously assemble in vitro into empty spherical capsids, electron microscopy images show that there is a non-negligible population of disordered nucleoprotein complexes that coexist with well-formed spherical viruses. Additionally, TR-SAXS kinetic data suggest that the protein-nucleic acid assembly undergoes a structural reorganization in which the capsid proteins make the nucleoprotein complexes more compact as they simultaneously bind the RNA. Upon acidification, the particles are well-formed viruses as suggested by electron microscopy images. These findings suggest that the encapsulation of RNA into well-formed viruses is likely a two-step assembly with a binding step and an acidification step.
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