The amount of Nck rather than N-WASP correlates with the rate of actin-based motility of Vaccinia virus.

Vaccinia virus is a large double-stranded DNA virus and a close relative of Mpox and Variola virus, the causative agent of smallpox. During infection, Vaccinia hijacks its host's transport systems and promotes its spread into neighboring cells by recruiting a signaling network that stimulates actin polymerization. Over the years, Vaccinia has provided a powerful model to understand how signaling networks regulate actin polymerization. Nevertheless, we still lack important quantitative information about the system, including the precise number of viral and host molecules required to induce actin polymerization. Using quantitative fluorescence microscopy techniques, we have determined the number of viral and host signaling proteins accumulating on virions during their egress. Our analysis has uncovered two unexpected new aspects of this process: the number of viral proteins in the virion is not fixed and the velocity of virus movement depends on the level of a single adaptor within the signaling network.