When a host cell is infected, the Paramyxoviridae family  (to which the measles virus belongs) protect their RNA genomes in nucleocapsids, very long helical structures made up of thousands of nucleo-proteins. The nucleocapsid formation process is essential for viral replication, and, as such, it presents a potentially promising drug target to treat these infections.

Until now, it has not been possible to shed light on the assembly process of these nucleocapsids ("encapsidation”), since the process could not be monitored in vitro. In this study, for the first time, researchers from IBS in Grenoble describe how this assembly occurs, using a combination of several techniques, such as nuclear magnetic resonance, fluorescence spectroscopy and electron microscopy.

By combining all these technologies, it was possible to monitor nucleocapsid assembly: adding RNA molecules to a protein isolate solution, which self-assembled on the RNA scaffolding. The researchers were then able to observe the assembly process in real-time, i.e. the in vitro duplication of what happens in an infected cell immediately after replication of the viral genome. The researchers then discovered that nucleocapsid assembly depends on the exact RNA sequence, a very surprising observation given that it is always necessary for the virus to fully protect its genome, whatever sequence is considered.

This new research tool not only makes it possible to study the basis of molecular interaction between nucleo-proteins and RNA, but it also paves the way for several new applications. The potential for monitoring the effectiveness of genome encapsidation in different conditions could develop viral replication inhibitors, and gives hope for multiple applications in the nano-biotechnology sector or in the development of vaccinations.