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DNA extracted from Dane particles has been characterized by gel electrophoresis and restriction enzyme cleavage with endonuclease R-HaeIII (from Hemophilus aegyptius). Dane particle DNA is proposed to be a double-stranded circular DNA approximately 3600 nucleotides in length containing a single-stranded gap of 600-2100 nucleotides. The endogenous DNA polymerase (DNA nucleotidyl-transferase; deoxynucleosidetriphosphate:DNA deoxynucleotidyltransferase; EC 2.7.7.7) reaction appears to repair this single-stranded gap.

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.

Virus-associated particles have been isolated from the livers of three common gray tree squirrels (Sciurus carolinensis pennsylvanicus) that have histological evidence of hepatitis. Two of these livers were also positive by orcein staining, suggesting the presence of surface antigen in the cytoplasm of hepatocytes. Fractionation of these particles by CsCl density equilibrium gradient centrifugation and assay of the fractions for surface antigen, core antigen, and DNA polymerase activities demonstrate the presence of all three at an approximate density peak of 1.27. Electron microscopic examination of purified virus preparations showed spherical particles with a mean diameter of 25 nm. Initial characterization of the DNA polymerase product by gel electrophoresis showed a single DNase I sensitive band, migrating slightly faster than the woodchuck hepatitis virus DNA polymerase product. The presence of apparently cross-reacting antibodies was demonstrated by purified hepatitis B surface and/or core antigens binding to some squirrel sera in solid phase assays. Infected tree squirrels appear to lack detectable antigen in their sera. These results suggest that the tree squirrels studied are chronic carriers of a hepatitis B type virus. The host-virus interaction described herein may be useful in understanding the chronic carrier state associated with hepatitis B in man.