NS4 A/B are two of the seven nonstructural (NS) proteins making up the HCV polyprotein. The NS proteins recruit the viral genome into an RNA replication complex, which is associated with rearranged cytoplasmic membranes. NS4A acts as a cofactor with the NS3 serine protease and stabilizes its folding. The NS3-NS4A complex is essential for the activation of the latter and allows membrane anchorage of NS3.
HCV is a positive, single-stranded RNA virus in the Flaviviridae family. The genome is approximately 10,000 nucleotides and encodes a single polyprotein of about 3,000 amino acids.
HCV is responsible for a large proportion of worldwide chronic viral hepatitides. Most of these infections develop into chronic hepatitis, which often progresses to liver cirrhosis and hepatocellular carcinoma. At present, (unlike hepatitis A and B), there is no vaccine to prevent hepatitis C infection.
The hepatitis C virus (HCV) nonstructural protein 4B (NS4B) is a relatively hydrophobic 27-kDa protein. The 4A protein has a molecular weight of 6 kDa.