Our results demonstrate that the C-terminal domain of hnRNP A1, including the M9 sequence and the glycinerich region, is important for MHV RNA transcription and replication, but the mechanism of the dominant-negative effects of hnRNP A1DC is still not clear. hnRNP A1DC retains the RNA-binding and self-association ability and is capable of binding the viral proteins N and p22, which are associated with the transcription/replication complex. It is possible that hnRNP A1DC is not productive due to its inability to interact with other viral or cellular proteins that are involved in MHV RNA synthesis. We have found a protein of~250 kDa that binds only the wt, but not the mutant hnRNP A1 ( Figure 7D ). It remains to be shown whether this cellular protein is involved in MHV RNA synthesis.