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J Virol, April 1998, p. 3051-3059, Vol. 72, No. 4
Laboratory of Infectious Diseases, National
Institute of Allergy and Infectious Diseases, National Institutes of
Health, Bethesda, Maryland
Received 27 August 1997/Accepted 5 December 1997
Feline calicivirus (FCV), a member of the
Caliciviridae, produces its major structural protein as a
precursor polyprotein from a subgenomic-sized mRNA. In this study, we
show that the proteinase responsible for processing this precursor into
the mature capsid protein is encoded by the viral genome at the
3'-terminal portion of open reading frame 1 (ORF1). Protein expression
studies of either the entire or partial ORF1 indicate that the
proteinase is active when expressed either in in vitro translation or
in bacterial cells. Site-directed mutagenesis was used to characterize the proteinase Glu-Ala cleavage site in the capsid precursor, utilizing
an in vitro cleavage assay in which mutant precursor proteins
translated from cDNA clones were used as substrates for trans cleavage by the proteinase. In general, amino acid
substitutions in the P1 position (Glu) of the cleavage site were less
well tolerated by the proteinase than those in the P1' position (Ala).
The precursor cleavage site mutations were introduced into an
infectious cDNA clone of the FCV genome, and transfection of RNA
derived from these clones into feline kidney cells showed that
efficient cleavage of the capsid precursor by the virus-encoded
proteinase is a critical determinant in the growth of the virus.
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Cleavage of the Feline Calicivirus Capsid Precursor
Is Mediated by a Virus-Encoded Proteinase
*
Corresponding author. Mailing address: 9000 Rockville
Pike, Building 7, Room 137, Bethesda, MD 20892. Phone: (301) 496-5811. Fax: (301) 496-8312. E-mail: kgreen{at}atlas.nih.gov.
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