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J Virol, February 1998, p. 1677-1682, Vol. 72, No. 2
Asian Center for Bioresources and
Environmental Sciences, University of Tokyo, Bunkyo-ku, Tokyo,
Japan; Division of Biology, California Institute of Technology,
Pasadena, California; and Center for Agricultural Molecular
Biology, Cook College, Rutgers University, New Brunswick, New Jersey
Received 2 June 1997/Accepted 25 October 1997
RNA 2 of soil-borne wheat mosaic virus (SBWMV), the type species of
the genus Furovirus, encodes a protein previously
hypothesized to be initiated at an in-frame non-AUG codon upstream of
the AUG initiation codon (nucleotide positions 334 to 336) for the
19-kDa capsid protein. Site-directed mutagenesis and in vitro
transcription and translation analysis indicated that CUG (nucleotides
214 to 216) is the initiation codon for a protein with a calculated
molecular mass of 25 kDa composed of a 40-amino-acid extension to the N terminus of the 19-kDa capsid protein. A stable deletion mutant, which
was isolated after extensive passages of a wild-type SBWMV, contained a
mixture of two deleted RNA 2's, only one of which coded for the 25-kDa
protein. The amino acid sequence of the N-terminal extension was
moderately conserved and the CUG initiation codon was preserved among
three SBWMV isolates from Japan and the United States. This amino acid
sequence conservation, as well as the retention of expression of the
25-kDa protein in the stable deletion mutant, suggests that the 25-kDa
protein is functional in the life cycle of SBWMV. This is the first
report of a non-AUG translation initiation in a plant RNA virus genome.
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Non-AUG Translation Initiation in a Plant RNA
Virus: a Forty-Amino-Acid Extension Is Added to the N Terminus of
the Soil-Borne Wheat Mosaic Virus Capsid Protein
*
Mailing address: Asian Center for Bioresources and
Environmental Sciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku,
Tokyo 113, Japan. Phone and fax: 81-3-5800-5192. E-mail:
shirako{at}ims.u-tokyo.ac.jp.
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