The sequences encompassing the RT site and the predicted 3 0 stem-loop structure for VEEV and SINV were synthesized by GenScript and cloned into the XhoI and BglII sites of pDluc, a derivative of the p2luc vector (61, 62) . The firefly luciferase gene is in the same reading frame relative to the upstream renilla luciferase gene such that RT of the stop codon results in a renilla-firefly luciferase fusion product. Derivative constructs were generated by PCR using appropriate primers and recloning into pDluc. All plasmids were verified by DNA sequencing.