Alphaviral non-structural protein-host RBP co-condensation as a mechanism to sustain virus replication

It has long been recognized that the intracellular replication of alphaviruses critically relies on several key host RNA-binding proteins (RBPs), including G3BP1/2 and FXR1/FXR2/FMR1. But how these RBPs modulate alphaviral replication, and whether it would be possible to target them for antiviral treatment, is less explored. Here, using Semliki Forest virus (SFV) as a model, we report that SFV non-structural protein 3 (nsP3) exploits G3BP to drive its condensation and transforms antiviral stress granules into proviral nsP3-G3BP co-condensates. The gel-like co-condensates enrich and protect viral genomic RNAs from host RNase degradation and promote viral translation and replication. nsP3-RBP co-condensation is widespread among alphaviruses, and condensate disruption is a plausible antiviral approach. Thus, these findings uncover a general anti-alphavirus strategy based on the conserved reliance of virus-host protein co-condensation.