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Journal of Virology, October 1998, p. 8013-8020, Vol. 72, No. 10
Institute for Medical Microbiology, Medical
University of Lübeck, 23538 Lübeck, Germany
Received 3 March 1998/Accepted 9 July 1998
Proteolytic processing of the picornaviral polyprotein mediated by
the differential action of virus-encoded proteinase(s) is pivotal to
both RNA genome replication and capsid formation. Possibly to enlarge
the array of viral proteins, picornaviral polyprotein processing
results in intermediate and mature products which apparently have
distinct functions within the viral life cycle. For hepatitis A virus
(HAV), we report here on the autoproteolysis of precursor
polypeptides comprising the only viral proteinase, 3Cpro, and on their role in viral particle formation.
Following transient expression of a nested set of
3Cpro-containing proteins (P3, 3ABC, 3BCD, 3CD, 3BC, and
3C) in eukaryotic cells, the extent of processing was determined by
analyzing the cleavage products. The 3C/3D site was more efficiently
cleaved than those at the 3A/3B and 3B/3C sites, leading to the
accumulation of the intermediate product 3ABC. In the absence of 3A
from the precursor, cleavage at the 3B/3C site was further reduced and a switch to an alternative 3C/3D site was observed. Coexpression of various parts of P3 with the precursor of the viral structural proteins P1-2A showed that all 3C-containing intermediates cleaved P1-2A with almost equal efficiency; however, viral particles carrying the neutralizing epitope form much more readily in the presence of the
complete P3 domain than with parts of it. These data support the notion
that efficient liberation of structural proteins from P1-2A is
necessary but not sufficient for productive HAV capsid formation and
suggest that the polypeptides flanking 3Cpro
promote the assembly of viral particles.
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Processing of Proteinase Precursors and Their
Effect on Hepatitis A Virus Particle Formation
*
Corresponding author. Mailing address: Institute for
Medical Microbiology, Medical University of Lübeck, Ratzeburger
Allee 160, 23538 Lübeck, Germany. Phone: 49-451-500 4085. Fax:
49-451-500 3637. E-mail: gaussmue{at}hygiene.mu-luebeck.de.
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