Adding purified recombinant eEF1Bc to CFE from tef4D yeast supported TBSV repRNA replication to similar extent as the CFE from wt yeast (i.e., containing wt eEF1Bc, Figure 1D , lanes 3-6 versus 1-2), indicating that the recombinant eEF1Bc can complement the missing Tef4p in vitro, when the same amount of p33 and p92 pol was provided. Using large amount of eEF1Bc in the CFE-based assay did not further increase TBSV repRNA replication ( Figure 1D , lanes 3-4), suggesting that eEF1Bc should be present in optimal amount during TBSV replication.