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The unique role of domain 2A of the hepatitis A virus precursor polypeptide P1-2A in viral morphogenesis.

The initial step during assembly of the hepatitis A virus particle is driven by domain 2A of P1-2A, which is the precursor of the structural proteins. The proteolytic removal of 2A from particulate VP1-2A by an as yet unknown host enzyme presumably terminates viral morphogenesis. Using a genetic approach, we show that a basic amino acid residue at the C-terminus of VP1 is required for efficient particle assembly and that host proteases trypsin and cathepsin L remove 2A from hepatitis A virus particles in vitro. Analyses of insertion mutants in the C-terminus of 2A reveal that this part of 2A is important for liberation of P1-2A from the polyprotein. The data provide the first evidence that the VP1/2A junction is involved in both viral particle assembly and maturation and, therefore, seems to coordinate the first and last steps in viral morphogenesis.