To test if eEF1Bc directly binds to a particular region within the TBSV repRNA, we performed electrophoretic mobility shift (EMSA) experiments with purified eEF1Bc and 32 P-labeled regions of (+)repRNA that included known cis-acting elements involved in (-)RNA synthesis [39, 40, 41] . These experiments revealed that eEF1Bc bound efficiently to the 39-end of the TBSV (+)repRNA (construct SL3-2-1, carrying the terminal 3 stem-loop structures, Figure S1 ). Template competition experiments confirmed that SL3-2-1 RNA bound competitively to eEF1Bc in vitro( Figure S1B ).