Two forms of the major barley stripe mosaic virus nonstructural protein are synthesized in vivo from alternative initiation codons.
Barley stripe mosaic virus (BSMV) has a tripartite genome comprising RNAs designated alpha, beta, and gamma, which collectively encode seven polypeptides. We show here that an antiserum raised against an abundant disease-specific protein from BSMV-infected plants reacts specifically with the viral beta b gene product expressed as part of a beta-galactosidase fusion protein in Escherichia coli. Two predominant forms of the protein, beta b and beta b', are synthesized in vivo. Infectious in vitro transcripts derived from wild-type and mutant BSMV cDNA clones have been used to map the initiation site for translation of the beta b protein in vivo. The results of our mutagenesis experiments are consistent with a model in which translation of the beta b' protein is initiated by ribosomes that scan past the 5'-proximal beta b initiation site. A mutant which is able to synthesize only the shorter beta b' protein was indistinguishable from the wild-type with respect to all of the phenotypes tested. Thus, the beta b form of the protein is dispensable in planta, and whether the two forms of the protein have different functions in vivo is unclear at present.
Petty
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IT
Department of Plant Pathology, University of California, Berkeley 94720.
Jackson
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D000595:Amino Acid Sequence; D001483:Base Sequence; D002213:Capsid / Q000096:biosynthesis / Q000235:genetics* / Q000302:isolation & purification; D003062:Codon / Q000235:genetics*; D005814:Genes, Viral; D001467:Hordeum; D008969:Molecular Sequence Data; D009029:Mosaic Viruses / Q000235:genetics*; D009154:Mutation; D012333:RNA, Messenger / Q000235:genetics*; D012367:RNA, Viral / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000302:isolation & purification; D015183:Restriction Mapping; D014758:Viral Core Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000302:isolation & purification; D017361:Viral Nonstructural Proteins; D001616:beta-Galactosidase / Q000235:genetics / Q000302:isolation & purification
D003062:Codon; D012333:RNA, Messenger; D012367:RNA, Viral; D011993:Recombinant Fusion Proteins; D014758:Viral Core Proteins; D017361:Viral Nonstructural Proteins; D001616:beta-Galactosidase