Mutational analysis of a virulence locus in the E2 glycoprotein gene of Sindbis virus

The substitution of arginine for serine at position 114 of glycoprotein E2 in several biological and recombinant Sindbis virus mutants was shown previously to attenuate the virus for neonatal mice and also to accelerate virus penetration into BHK cells. To further examine the genetically linked effects on both virus penetration into cultured cells and pathogenesis in vivo, mutants containing each of 16 different amino acid coding changes at this position were generated by site-directed mutagenesis of a full-length cDNA clone of the Sindbis virus genome. Viable virus was recovered following transfection of RNA transcripts from 14 of the clones. Phenotypic analysis of these virus mutants revealed that specific amino acid residues affected either the pathogenesis or penetration phenotype independently or both phenotypes simultaneously. Thus, both the position of a mutation within the E2 sequence and the particular amino acid encoded at that position are important determinants of the mutant phenotypes.