Fusion protein corresponding to the serine protease NS3 (a.a. 3-181) and cofactor NS4A (a.a. 21-32) from Hepatitis C virus genotype 1b (GenBank Accession No. AF054247) with Arg-to-Gln mutation on a.a. 155, an N-terminal FLAG-His tag, and a 4 a.a. linker, MW = 22.3 kDa, expressed in an E. coli expression system.