Large surface proteins of hepatitis B virus containing the pre-s sequence

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Abstract
The sequence of hepatitis B virus DNA contains an open reading frame which codes for a not-yet-identified protein of at least 389 amino acids. Only the products starting at the 3rd (GP33/GP36) or the 4th (P24/GP27) initiation signal have been characterized as components of the viral surface antigen. A larger protein, P39, and its glycosylated form, GP42, were found in hepatitis B virus particles and viral surface antigen filaments. Immunological cross-reactions showed that P39/GP42 is partially homologous to P24/GP27 and GP33/GP36. The unique portion of its sequence bound monoclonal antibodies which had been induced by immunization with hepatitis B virus particles. Proteolytic cleavage patterns and subtype-specific size differences suggested that the sequence of P39 starts with the 1st initiation signal of the open reading frame. Its amino-terminal part (pre-s coded) is exposed at the viral surface and, probably, is highly immunogenic. A model is presented of how the open reading frame for the viral envelope leads to defined amounts of 3 different proteins.