Figure 1 Electron micrograph of purified particles of Barley stripe mosaic virus (BSMV), stained with 2% uranyl acetate. The particles are approximately 20 nm wide and have a length that varies depending on the size of the encapsidated RNA. The field was selected to represent monomers, but often a range of heterodisperse end to end aggregates up to 1,000 nm in length predominate in various purified preparations. The particles in the top right, bottom center, and upper right side of the micrograph are end to end aggregates that occur during purification. The bar represents 150 nm.
Figure 2 Genome organization of Barley stripe mosaic virus (BSMV). The shaded rectangles and solid rectangles represent the ORFs and the 3-terminal tRNA-like structure, respectively. Each RNA is capped at the 5 terminus with a 7-methylguanosine residue. The 3 proximal ORFs on each RNA terminate with a UAA codon that initiates the short poly(A)n tract that directly precedes the 238 nts tRNA-like terminus. RNA encodes a single protein, a, with an amino-terminal methyltransferase domain (Mt) and a carboxy-terminal helicase domain (Hel). This protein is referred to as the helicase subunit of the replicase (RNA-dependent RNA polymerase). RNA encodes five proteins: a, the CP; b, a 58 103 protein that contains a helicase domain (Hel) and is translated from sgRNA1; c, a 17 103 protein that is separated from the b ORF by 173 nts; d, a 14 103 protein that overlaps the b and the c ORFs; and d, a 23 103 translational extension product of unknown function. The d, d, and c proteins are translated from the sgRNA2. RNA encodes two proteins. The a protein contains the GDD domain and is the polymerase subunit of the replicase. The cysteine-rich 17 103 b protein, which is translated from a sgRNA, has RNA binding ability.
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