Translation of the genes for the structural proteins of alphaviruses.

Synthesis of the structural proteins of Semliki Forest virus by a cell-free system derived from mouse L-cells and programmed by intracellular 26S RNA is described. This polycistronic RNA is translated in vitro into several discrete polypeptides. The identity of these polypeptides as the structural proteins of the virus was established by polyacrylamide gel electrophoresis, immunoprecipitation and tryptic peptide mapping. Studies using formyl--e135S]methionyl-tRNAf as precursor, and using diphtheria toxin and NAD to inhibit elongation, showed that 26S RNA contains only a single initiation site at, or near, the 5' end of the core protein cistron. Experiments in infected cells under conditions of synchronous initiation revealed that the order of the structural protein genes in 26S RNA is core-E3-E2-E1 in the 5' leads to 3' direction.