Evidence that Tomato Spotted Wilt Virus RNA is a Positive Strand

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Abstract
Summary RNA of tomato spotted wilt virus (TSWV) was analysed by gel electrophoresis on methylmercury-agarose gels. Three segments were detected with mol. wt. of 2·7 × 106, 1·7 × 106 and 1·1 × 106. The behaviour on oligo(dT)-cellulose columns indicated that TSWV RNA does not contain poly(A) sequences. TSWV RNA directed the synthesis of several proteins in a wheatgerm cell-free system and a messenger-dependent rabbit reticulocyte lysate. Analysis of the translation products by gel electrophoresis revealed that two major polypeptides were synthesized in both systems. One could be identified by immunoprecipitation as the nucleocapsid protein; the identity of the other, having a mol. wt. of 60000, is unknown. The above results demonstrate that TSWV contains a positive-stranded RNA and this conclusion was confirmed by other experiments. TSWV RNA labelled with 125I did not hybridize with polyribosomal RNA from infected leaves and transcriptase activity could not be detected in purified preparations of TSWV or in nucleocapsid extracts from infected leaves. This study supports the view that TSWV is a unique membrane-bounded plant virus whose genome consists of three RNA segments which act as mRNA.