Visualization and characterization of GB virus-C particles: evidence for a nucleocapsid.

GB virus type C (GBV-C) is a member of the hepacivirus genus within the Flaviviradae. Persistent GBV-C infection is common in humans, yet it remains unclear if GBV-C causes any disease. Although GBV-C infection has been associated with acute non-A to non-E post-transfusion hepatitis, it does not appear to cause chronic hepatitis. GBV-C is closely related to hepatitis C virus (HCV), but indirect evidence suggests that it does not encode a core protein at the amino terminus of the open reading frame (ORF). This has led to speculation that GBV-C does not have a nucleocapsid. We evaluated the buoyant density of GBV-C, and found very low density particles consistent with virions, and intermediate density particles consistent with nucleocapsids in GBV-C-infected people. In addition, electron microscopy demonstrated an apparent nucleocapsid within an enveloped particle. Although these biophysical data strongly suggest that GBV-C utilizes a nucleocapsid, they do not indicate the origin of the protein content of this particle. To assess this, we evaluated patient plasma for reactivity with a synthetic oligopeptide representing a conserved region near the amino terminus of the predicted ORF. Specific antibody was detected in some individuals, similar to data of Feucht et al. who identified antibody against a recombinant core protein in GBV-C-infected people. These data indicate that GBV-C particles contain nucleocapsids. At least in some patients, the region upstream of the GBV-C E1 protein coding region appears to be expressed, and this region may represent the structural protein of the nucleocapsid.