Mapping and expression of southern bean mosaic virus genomic and subgenomic RNAs.
The coat protein of the cowpea strain of southern bean mosaic sobemovirus (SBMV-C) is translated from a subgenomic RNA (sgRNA) that is synthesized in the virus-infected cell. Like the SBMV-C genomic RNA, the sgRNA has a viral protein (VPg) covalently bound to its 5' end. The mechanism(s) by which ribosomes initiate translation on the SBMV-C RNAs is not known. To begin to characterize the translation of the sgRNA it was first necessary to precisely map its 5' end. Primer extension was used to identify SBMV-C nucleotide (nt) 3241 as the transcription start site. As a control, the 5' end of the genomic RNA was also mapped. Surprisingly, the 5' terminal nt of this RNA was identified as SBMV-C nt 2. The primary structure of the 5' ends of these two RNAs is therefore expected to be VPg-ACAAAA. Precise mapping of the 5' end of the sgRNA of the bean strain of SBMV (SBMV-B) demonstrated that it has these same elements. Translation of coat protein from the SBMV-C sgRNA and p21 from the SBMV-C genomic RNA was compared using a cell-free system. The results of these experiments were consistent with translation of these proteins by a 5' end-dependent scanning mechanism rather than by internal ribosome binding.
Hacker
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Department of Microbiology and Center for Legume Research, University of Tennessee, Knoxville 37996-0845, USA. hacker@utk.edu
Sivakumaran
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D001483:Base Sequence; D002874:Chromosome Mapping; D007887:Fabaceae / Q000821:virology*; D015967:Gene Expression Regulation, Viral; D016679:Genome, Viral; D008969:Molecular Sequence Data; D009029:Mosaic Viruses / Q000235:genetics*; D010946:Plants, Medicinal; D012367:RNA, Viral / Q000235:genetics*
D012367:RNA, Viral