Production of high-quality, well-characterized recombinant proteins facilitates 
screening of compound libraries. The protocols detailed in this unit are used to 
purify three recombinant enzymes that are widely used in HCV research: the HCV 
NS3 protease domain, the helicase domain as an NS3+NS4A complex, and the NS5B 
RNA-dependent RNA polymerase. The active enzymes are purified to homogeneity by 
two-column chromatography to support a screening program for HCV inhibitors.