To know the effects of the nucleotide difference at M847 on biological properties of the virus, we have recovered ZH501 carrying A at M847 (rZH501-M847-A) and that carrying G (rZH501-M847-G) at the corresponding site using a reverse genetics system of ZH501, in which endogenously expressed T7 polymerease in BHK/T7-9 cells drives expression of viral RNAs and proteins from the transfected plasmids. Sequence analysis of the entire L, M and S RNA segments of rZH501-M847-A and rZH501-M847-G revealed that both viruses had the expected primary sequences.