The C-Terminal Repeat Domains of nsP3 from the Old World Alphaviruses Bind Directly to G3BP

The Old World alphaviruses block stress granule assembly by sequestration of RasGAP SH3-domain binding protein (G3BP). Here, we show that the proline-rich sequences in the hypervariable domain of nonstructural protein 3 (nsP3) of both Semliki Forest virus and Chikungunya virus were dispensable for binding to G3BP. nsP3 variants with or without this domain colocalized with G3BP. Furthermore, we show that the C-terminal repeat motifs of nsP3 were sufficient for G3BP binding.