Comparative analysis of polypeptides synthesized in vivo and in vitro by two strains of barley stripe mosaic virus

Proteins synthesized in a wheat germ system containing RNA from the Type or ND18 strain of barley stripe mosaic virus (BSMV), or polyribosomes from Type or ND18-infected barley, were compared with each other and with polypeptides from Type and ND18-infected plants. Polypeptides with apparent molecular weights (M r) of 25, 67, and 120 × 10 3 that were induced in infected barley were synthesized in vitro by polyribosomes from infected plants or RNA from purified BSMV. The 25,000 M r polypeptide was identified as BSMV coat protein by coelectrophoresis with coat protein from purified virions, by immunoprecipitation, and by absence of [ 35S]methionine incorporation into the protein. Strain-specific differences were observed in two additional translation products synthesized in both wheat germ and reticulocyte lysate systems containing Type of ND18 RNA. RNAs from both strains directed synthesis of 71 and 82 × 10 3 M r polypeptides. However, ND18 RNA directed synthesis of a larger amount of the 71,000 M r polypeptide, whereas with Type RNA the 82,000 M r polypeptide predominated. These two proteins may be processed in vivo because reduced synthesis of both polypeptides in wheat germ extracts containing polyribosomes from infected plants was correlated with increased synthesis of the 67,000 M r polypeptide. Several additional polypeptides synthesized in the wheat germ system were probably premature termination products because their synthesis in the reticulocyte lysate was greatly reduced.