A biochemical comparison of the in vitro replication of a virulent and an avirulent strain of Venezuelan encephalitis virus.

The virulent Venezuelan equine encephalitis (VEE) virus strain, Trinidad donkey (TRD) and its vaccine derivative strain TC-83, demonstrated biological and biochemical differences in their replication. These two viruses had similarly shaped growth curves; however, TRD virus-infected cells produced significantly more infectious virus than did the TC-83 virus-infected cells during the very early period of the replication cycle. TRD virus inhibited host cell protein synthesis in Vero cells earlier than did TC-83 virus as measured by the incorporation of [35S]methionine into cellular proteins. Virus-specified proteins were detected 1 to 2 h earlier in TRD virus-infected cells than in the TC-83 virus-infected cells; however, pulse-chase studies failed to show differences in the processing of the viral structural proteins in cells infected by either of the viruses. TRD virus-infected cells produced more virus RNA than did the TC-83 virus-infected cells, and analysis of the intracellular viral RNA species showed an increased synthesis of 26S RNA in the TRD virus-infected cells. The difference in amounts of 26S virus RNA produced was most pronounced early during the infection and may explain why TRD virus infection resulted in an earlier production of viral proteins and inhibition of cellular protein synthesis than was observed in the cells infected with the avirulent vaccine strain of VEE virus.