THE MIDDLE HEPATITIS-B VIRUS ENVELOPE PROTEIN IS NOT NECESSARY FOR INFECTIVITY OF HEPATITIS-DELTA VIRUS

The hepatitis delta virus (HDV) envelope contains the large (L), middl e (hi), and small (S) surface proteins encoded by coinfecting hepatiti s B virus. Although HDV-like particles can be assembled with only the S protein in the envelope, the L protein is essential for infectivity in vitro (C. Sureau, B. Guerra, and R. Lanford, J. Virol. 67:366-372, 1993). Here, we demonstrate that the M protein, previously described a s carrying a site for binding to polymerized human albumin, is not nec essary for infectiuit;v. HDV-like particles coated with the S plus L o r the S plus hi plus L proteins are infectious in primary cultures of chimpanzee hepatocytes. We conclude that the S and L proteins serve tw o essential functions in the HDV replication cycle; the S protein ensu res the export of the HDV genome from an infected cell by forming a pa rticle, and the L protein ensures its import into a human hepatocyte.