Highly purified cucumber mosaic virus-induced RNA-dependent RNA polymerase does not contain any of the full length translation products of the genomic RNAs.

The extensively purified RNA-dependent RNA polymerase (RNA replicase) induced by infection of cucumber seedlings with cucumber mosaic virus (CMV) was investigated to determine whether the enzyme contains full-length translation products of the CMV genomal RNAs. Two experimental approaches were used. (1) RNA replicase preparations from plants infected with three strains of CMV (Q, P, and T) all had almost identical polypeptide compositions, which included a major polypeptide of relative mobility on sodium dodecyl sulfate-polyacrylamide gels of Mr, 100,000, and two other proteins, Mr 110,000 and Mr, 35,000, present in smaller, varying amounts. These polypeptides were unique to enzyme preparations from CMV-infected plants and had similar electrophoretic mobilities to the translation products of Q-CMV RNAs 1, 2, and 3, respectively. Analysis of the in vitro translation products of the corresponding RNAs of the other two strains of CMV showed, however, that those of P-CMV RNA 2 and T-CMV RNAs 1 and 3 varied significantly in size from the translation products of the corresponding Q-CMV RNAs. (2) Peptide mapping studies, using digestion with the V8 protease from Staphylococcus aureus or cleavage with CNBr, confirmed that none of these three components of the highly purified RNA replicase was a translation product of the CMV RNAs. The work reported in this paper, therefore, showed that the full-length translation products of the genomal RNAs of CMV were absent from the RNA replicase induced by this virus after solubilization and extensive purification.