Site-specific mutations in the NS2 protein of epizootic haemorrhagic disease virus markedly affect the formation of cytoplasmic inclusion bodies.

The importance of a conserved amino acid motif in the nonstructural protein NS2 of different orbiviruses was investigated with regard to virus inclusion body (VIB) formation. A number of epizootic haemorrhagic disease virus NS2 deletion and substitution mutants were prepared and expressed as baculovirus recombinants. Deletion of the motif or substitution of at least three residues within the region, had a detrimental effect on VIB formation in insect cells. Furthermore, these NS2 mutants were not complexed with single-stranded RNA in infected cells and appeared to be cytotoxic. Cumulatively, the results suggest that this motif is an essential structural determinant for NS2 function.