Tree squirrel hepatitis B virus: antigenic and structural characterization.

Tree squirrel hepatitis B virus (THBV)-associated particles isolated from the livers of naturally infected animals share one or more antigenic determinants with hepatitis B surface antigen in solid-phase immunoassays. Characterization of THBV-associated polypeptides by sodium dodecyl sulfate/polyacrylamide gel electrophoresis reproducibly demonstrated major components with apparent sizes of 15.5 and 17 kDa. Peptide mapping of these components shows that they are related to the peptide maps of the major surface antigen polypeptides associated with hepatitis B virus and like viruses. Sodium dodecyl sulfate/polyacrylamide gel analysis also demonstrated discrete bands at 14.5, 19, 20, and 35 kDa. Upon blotting of THBV-associated polypeptides with sera containing antibodies to hepatitis B core antigen or hepatitis B X antigen, only the 35-kDa band became detectable, suggesting that this component is core related. These results establish the presence of both surface and core antigen-related polypeptides associated with purified THBV and better define the relationship of THBV to the family of hepatitis B virus and like viruses.