Expression and characterization of HCV NS3 protease

The overexpression of a gene in a heterologous system is often the prelude to or the prerequisite of the elucidation and characterization of a given protein, in particular where the protein is difficult to obtain in sufficient quantity from natural sources. Prokaryotic expression systems, in particular Escherichia coli have been exploited successfully for a number of viral proteins. A large number of E. coli expression systems are currently commercially available that offer the investigator a large number of choices with regard to promoter choice, site of expression, fusions, and so forth. Since the variety and number of expression systems available are extensive, it is not within the scope of this chapter to discuss them fully, and the final choice of expression system used, is often arrived at empirically and often reflects the investigator's "favored system."