We confirmed a direct role for eEF1Bc in RNA synthesis in vitro by using a cell-free extract prepared from tef4D yeast that supported (-)-strand RNA synthesis ,3-fold less efficiently than CFE from wt yeast (Figure 1 ). Moreover, in vitro assays with highly purified eEF1Bc and the recombinant TCV RdRp, which is closely homologous with the TBSV p92 pol , also revealed that eEF1Bc stimulates (-)-strand synthesis by binding to the viral (+)RNA template ( Figure 3) . Accordingly, pre-incubation of eEF1Bc and the TBSV-derived template RNA prior to the RdRp assay led to the highest level of stimulation of (-)RNA synthesis ( Figure 2 ). On the other hand, eEF1Bc does not stimulate the RdRp activity directly, since pre-incubation of eEF1Bc with the RdRp did not lead to more efficient (-)-strand RNA synthesis in vitro ( Figure 2 ). We propose that eEF1Bc modifies the structure of the (+)-strand template prior to initiation of (-)-strand synthesis that leads to more efficient RNA synthesis as described below.