Abstract
Nucleotide sequences of the structural protein genes (5'-capsid-E3-E2-6K-E1-3') of the virulent Trinidad donkey (TRD) strain of Venezuelan equine encephalitis (VEE) virus and its attenuated vaccine derivative, strain TC-83, were determined from cDNA clones containing the 3'-one-third (26S RNA) region of the 42S RNA genomes of these viruses. The capsid, E3, and 6K genes contained no mutations, and therefore are not involved in the attenuation of TC-83 virus. One and five amino acid mutations in E1 and E2, respectively, and a single nucleotide deletion in the 3'-noncoding region of TC-83 virus were detected. The E2 mutations, which affected predicted secondary structure and hydropathicity, are probable determinants of the attenuated phenotype. TRD and TC-83 E2 proteins apparently are equally glycosylated at three sites. The structural protein genes of VEE TRD and TC-83 viruses were expressed in vaccinia virus under control of the vaccinia 7.5K promoter. Expression of seven E2-specific and two of four El-specific epitopes was shown by indirect immunofluorescence using monoclonal antibodies. Mice immunized with recombinant virus developed VEE virus-specific neutralizing antibodies and survived intraperitoneal challenge with virulent TRD, P676, 3880, and Everglades VEE viruses. However, unlike TC-83 vaccine virus, recombinant virus did not protect mice from intranasal challenge with TRD virus. These results suggest that the recombinant vaccine may be a vaccine candidate for equines and humans at risk of mosquito-transmitted VEE, but perhaps not for laboratory workers at risk of aerosol infection with VEE virus.