IDENTIFICATION OF HEPATITIS-A VIRUS NONSTRUCTURAL PROTEIN 2B AND ITS RELEASE BY THE MAJOR VIRUS PROTEASE 3C

The RNA genome of hepatitis A virus (HAV) encodes a giant polyprotein that is putatively cleaved proteolytically into four structural and se ven non-structural proteins. So far, most of the proposed non-structur al proteins and their respective cleavage sites have not been identifi ed. A vaccinia virus recombinant (vRGORF) containing the complete HAV ORF under the control of the bacteriophage T7 promoter was used to exp ress HAV in recombinant animal cells (BT7-H) that constitutively expre ssed T7 DNA-dependent RNA polymerase. A HAV-specific 27.5 kDa expressi on product was identified as peptide 2B. The 27.5 kDa 2B antigen was a lso found in HAV-infected MRC-5 cells. The N-terminal amino acid resid ues of the new peptide 2B are Ala-Lys-Ile-Ser-Leu-Phe and polyprotein cleavage between 2A and 2B occurred at amino acids 836-837 (Gln-Ala). Furthermore, heterologous expression in the same system of regions P1- P2 and of the protease 3C (3C(pro)) gene, showed that P1-P2 polyprotei n is not cleaved autocatalytically but by 3C(pro). Hence, 3C(pro) is e ffective in cleaving the polyprotein 2A-2B junction.