Cell-free translation of soil-borne wheat mosaic virus RNAs

The genome of soil-borne wheat mosaic (SBWMV) virus appears to be composed of two RNAs. Three strains have the same large RNA, designated 1.0L RNA, but differ in the size of the smaller RNA, designated 0.5L RNA for wild type (WT), 0.4L RNA for mutant Lab 2, and 0.35L RNA for mutant Lab 1, where L corresponds to approximately 6700 nucleotide residues. The major translation products of 1.0L RNA in rabbit reticulocyte lysates had apparent molecular weights of 180,000 (180K), 152K, 135K, 80K, and 45K. None of these were precipitated with antiserum against virions. The 0.5L RNA stimulated the synthesis of products of 90K, 28K, and 19.7K, the 0.4L RNA of 66K, 28K, and 19.7K, the 0.35L RNA of 55K, 28K, and 19.7K. Protein of 19.7K comigrated with viral coat protein and was the predominant product in all cases. Immunoprecipitation, peptide mapping, and the time course of appearance of products suggest that the larger products of RNA Its (0.5L, 0.4L, and 0.35L RNA) arise from readthrough. The pattern of products is consistent with formation of 0.4L and 0.35L by internal deletions in the 3' region of 0.5L RNA. Extracts of SBWMV-WT-infected wheat contained polypeptides that corresponded to the translation products of 0.5L RNA in electrophoretic mobility and immunological reactivity.