STRUCTURAL LOCALIZATION OF THE E3 GLYCOPROTEIN IN ATTENUATED SINDBIS VIRUS MUTANTS

We have determined the three-dimensional structures of the wild-type S indbis virus and two of its mutants that retain the E3 sequence within PE2, Using difference imaging between these mutants and the wild-type virus, we have assigned a location for the 64-amino-acid sequence cor responding to E3 in the mutant spike complex. In the wild-type virus, the spike is composed of an E1-E2 heterotrimer. The E3 protein was fou nd to protrude midway between the center of the spike complex and the tips, Based on these results and the work of others, we propose a dist ribution for the Functional domains of the spike proteins within the s tructure of wild-type Sindbis virus. Within the structure of the virus , the El domains form the central portion of the spike complex, while the tips are formed by the E2 domains that Bare out from the center of the complex, The structural similarity between these Sindbis virus mu tants and Ross River virus suggests that E3 may also be present in the latter, which is also a member of the Alphavirus genus.