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J. Virol., Feb 1997, 900-909, Vol 71, No. 2
PJ Bonilla, SA Hughes and SR Weiss
The 21.7-kb replicase locus of mouse hepatitis virus strain A59 (MHV- A59)
encodes several putative functional domains, including three proteinase
domains. Encoded closest to the 5' terminus of this locus is the first
papain-like proteinase (PLP-1) (S. C. Baker et al., J. Virol. 67:6056-6063,
1993; H.-J. Lee et al., Virology 180:567-582, 1991). This cysteine
proteinase is responsible for the in vitro cleavage of p28, a polypeptide
that is also present in MHV-A59-infected cells. Cleavage at a second site
was recently reported for this proteinase (P. J. Bonilla et al., Virology
209:489-497, 1995). This new cleavage site maps to the same region as the
predicted site of the C terminus of p65, a viral polypeptide detected in
infected cells. In this study, microsequencing analysis of the radiolabeled
downstream cleavage product and deletion mutagenesis analysis were used to
identify the scissile bond of the second cleavage site to between Ala832
and Gly833. The effects of mutations between the P5 and P2' positions on
the processing at the second cleavage site were analyzed. Most
substitutions at the P4, P3, P2, and P2' positions were permissive for
cleavage. With the exceptions of a conservative P1 mutation, Ala832Gly, and
a conservative P5 mutation, Arg828Lys, substitutions at the P5, P1, and P1'
positions severely diminished second-site proteolysis. Mutants in which the
p28 cleavage site (Gly247 / Val248) was replaced by the Ala832 / Gly833
cleavage site and vice versa were found to retain processing activity.
Contrary to previous reports, we determined that the PLP-1 has the ability
to process in trans at either the p28 site or both cleavage sites,
depending on the choice of substrate. The results from this study suggest a
greater role by the PLP-1 in the processing of the replicase locus in vivo.
Copyright © 1997, American Society for Microbiology
Characterization of a second cleavage site and demonstration of activity in trans by the papain-like proteinase of the murine coronavirus mouse hepatitis virus strain A59
Department of Microbiology, University of Pennsylvania, Philadelphia 19104-6076, USA.
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