Hepatitis C virus (HCV) genotype 1b, also known as HCV1b, is a fusion protein of a.a. 21-32 of NS4A, linker (3 a.a.) and a.a. 31-181 of NS3 (GenBank Accession No. AF054247) with N-terminal FLAG-His-tag, MW = 22.3 kDa, expressed in an E. coli expression system.