Hepatitis C Virus RNA-Dependent RNA Polymerase (NS5B Polymerase)

The hepatitis C virus (HCV) chronically infects approx 4 million patients in the United States alone, and constitutes a major cause of chronic liver disease and hepatocellular carcinoma (1 –3 ). Current antiviral therapies for chronic hepatitis C remain relatively ineffective and have significant side-effects in many patients. Moreover, the lack of an easily reproducible tissue-culture system to propagate HCV has hampered the development of new antiviral therapies. Although detailed studies of several recombinant HCV nonstructural proteins have been initiated, our knowledge of the HCV NS5B polymerase that encodes an RNA-dependent RNA polymerase (RDRP) is rudimentary (4 –8 ). RNA-dependent RNA polymerases represent a class of viral enzymes that replicate the genomic RNA of plus strand RNA viruses (9 –11 ). A model enzyme of this group, the poliovirus RDRP encoded by the 3D^pol gene, has been extensively studied (12 –17 ). However, studies of recombinant hepatitis C virus RDRP (or NS5B polymerase) have only recently begun, and there is much to learn. A method is presented here for assaying HCV RDRP activity based on this laboratory’s experience with recombinant NS5B expressed in Escherichia coli and the experience of others studying NS5B expressed in insect cells (5 –8 ).