CHIMERIC SINDBIS-ROSS-RIVER VIRUSES TO STUDY INTERACTIONS BETWEEN ALPHAVIRUS NONSTRUCTURAL AND STRUCTURAL REGIONS

Sindbus virus and Ross River virus are alphaviruses whose nonstructura l proteins share 64% identity and whose structural proteins share 48% identity. Starting from full-length cDNA clones of both viruses, we ha ve generated two reciprocal Sindbus-Ross River chimeric viruses in whi ch the structural and nonstructural regions have been changed. These c himeric viruses replicate readily in several cell lines. Both chimeras grow more poorly than do the parental viruses, with the chimera conta ining Sindbis virus nonstructural proteins and Ross River virus struct ural proteins growing considerably better in both mosquito and Vero ce ll lines than the reciprocal chimera does. The reduction in replicativ e capacity in comparison with the parental viruses appears to result a t least in part from a reduction in RNA synthesis, which suggests that the structural proteins or sequence elements within the structural re gion interact with the nonstructural proteins or sequence elements wit hin the nonstructural region, that these interactions are required for efficient RNA replication, and that these interactions are suboptimal in the chimeras. The chimeras are able to infect mice, but their grow th is attenuated. Western equine encephalitis virus, a virus widely di stributed throughout the Americas, has been previously shown to have r isen by natural recombination between two distinct alphaviruses, but o ther naturally occurring recombinant alphaviruses have not been found. The present results suggest that most nonstructural/structural chimer as that might arise by natural recombination will be viable but that i nteractions between different regions of the genome, some of which wer e previously known but some of which remain unknown, limit the ability of such recombinants to become established.