Organization of the polyprotein precursor encoded in ORF1 of sapovirus clone pJG-SapI (GenBank accession no. [GB acc. No.] AY694184). (A) ORF1 encoding the nonstructural proteins (5,176 nucleotides in length) is shown. Putative cleavage sites are indicated. Both NS6 and NS6-7 proteins and their active-site mutant were expressed in Escherichia coli Rosetta(DE3) cells. The recombinant proteins bear a His6 tag at the C terminus. The nonstructural proteins NS1 to NS7 corresponding to the proteins p11, p28, 2C-like NTPase, p32, VPg, 3C-like protease, and 3D-like polymerase, respectively, are shown. (B) The proteins HA-[NS5/NS6]-NS6-7-His and HA-[NS4/NS5]-NS6-7-His bearing the authentic cleavage sites of the NS5-NS6 and the NS4-NS5 junctions, respectively, were expressed in Escherichia coli Rosetta(DE3) cells. Those constructs bear a His6 tag at the C terminus and an HA tag at the N terminus. The HA tag is underlined.