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Journal of Virology, March 1999, p. 2027-2037, Vol. 73, No. 3
Department of Virology, Leiden University
Medical Center, Leiden, The Netherlands1;
M. P. Chumakov Institute of Poliomyelitis and Viral
Encephalitides, Russian Academy of Medical Sciences, 142782 Moscow
Region, Russia2; and
Advanced Biomedical
Computer Center, SAIC/NCI-FCRDC, Frederick, Maryland
21702-12013
Received 2 September 1998/Accepted 10 December 1998
The open reading frame (ORF) 1b-encoded part of the equine
arteritis virus (EAV) replicase is expressed by ribosomal frameshifting during genome translation, which results in the production of an ORF1ab
fusion protein (345 kDa). Four ORF1b-encoded processing products, nsp9
(p80), nsp10 (p50), nsp11 (p26), and nsp12 (p12), have previously been
identified in EAV-infected cells (L. C. van Dinten, A. L. M. Wassenaar, A. E. Gorbalenya, W. J. M. Spaan, and E. J. Snijder, J. Virol. 70:6625-6633, 1996). In the
present study, the generation of these four nonstructural proteins was shown to be mediated by the nsp4 serine protease, which is the main
viral protease (E. J. Snijder, A. L. M. Wassenaar,
L. C. van Dinten, W. J. M. Spaan, and A. E. Gorbalenya, J. Biol. Chem. 271:4864-4871, 1996). Mutagenesis of
candidate cleavage sites revealed that Glu-2370/Ser, Gln-2837/Ser, and
Glu-3056/Gly are the probable nsp9/10, nsp10/11, and nsp11/12
junctions, respectively. Mutations which abolished ORF1b protein
processing were introduced into a recently developed infectious cDNA
clone (L. C. van Dinten, J. A. den Boon, A. L. M. Wassenaar, W. J. M. Spaan, and E. J. Snijder, Proc.
Natl. Acad. Sci. USA 94:991-997, 1997). An analysis of these mutants
showed that the selective blockage of ORF1b processing affected
different stages of EAV reproduction. In particular, the mutant with
the nsp10/11 cleavage site mutation Gln-2837
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Proteolytic Processing of the Open Reading Frame
1b-Encoded Part of Arterivirus Replicase Is Mediated by nsp4 Serine
Protease and Is Essential for Virus Replication
Pro displayed an unusual
phenotype, since it was still capable of RNA synthesis but was
incapable of producing infectious virus.
*
Corresponding author. Mailing address: Department of
Virology, Leiden University Medical Center, LUMC P4-26, P.O. Box 9600, 2300 RC Leiden, The Netherlands. Phone: 31 71 5261657. Fax: 31 71 5266761. E-mail: Snijder{at}Virology.azl.nl.
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