Poly(U) binding activity of hepatitis C virus NS3 protein, a putative RNA helicase

A non-structural protein of the hepatitis C virus (HCV), NS3, contains amino acid sequence motifs characteristic of serine-proteinases and RNA helicases. RNA binding activity of the NS3 protein with an apparent dissociation constant of 2 × 10−7 M was detected using a poly(U)-Sepharose resin. Competitive RNA binding analysis suggested that the NS3 protein binds preferentially to the poly(U) sequence, which is located at the 3′ end of HCV RNA. Mutational analysis of NS3 protein revealed the possibility that both the RNA helicase region and the serine-proteinase region were necessary for full RNA binding activity.