To demonstrate if the ATPase/helicase activity of Ded1p is important for the enhancement of TBSV RNA replication in the CFE-based replication assay, we tested an ATPase defective mutant of Ded1p (D1 mutant) [41] . This mutant could not enhance TBSV replication in vitro ( Figure 2C , lanes 1-2 versus 3-4), suggesting that the ATPase activity of Ded1p is important for TBSV replication.