p26 protein and 33-nm particle associated with nucleocapsid of hepatitis C virus recovered from the circulation of infected hosts.

Hepatitis C virus (HCV) has not yet been cultured or visualized. We attempted to recover HCV-associated particles from plasma of infected humans to assess the natural properties of the virus. Starting with 720 ml of donor plasma containing high titer of HCV core antigen ELISA activities, we identified HCV core antigen activity and viral RNA enriched in a potassium bromide density gradient fraction with a density of 1.115 g/ml. Icosahedron-shaped particles with an average diameter of 33 nm were liberated by treatment of the fraction with the detergent Tween 80. These particles were selectively visualized with an electron microscope using a grid coated with a murine monoclonal antibody directed to HCV core peptide and were also observed in aggregated forms with an immune electron microscope (IEM) with use of the anti-core antibody. An ultracentrifugation pellet of the above fraction was treated with sodium dodecyl sulfate (SDS) and 2-mercaptoethanol (2ME) and run in SDS-PAGE. A protein that bound antibodies directed to the predicted core protein of HCV was found at a molecular size estimated as about 26,000 Da, significantly greater than the 191 amino acid residues predicted from the presumed core gene of HCV. It is possible that translation initiation and/or the COOH-terminal cleavage site for HCV core protein in vivo may differ from estimates derived from the amino acid sequence of the polyprotein precursor. The nucleocapsid could also be chemically altered in the infected cell, resulting in a gel mobility different from the native protein.