We have used infectious in vitro transcripts from mutagenized turnip crinkle virus (TCV) cDNA clones to identify the gene products required for viral RNA replication, virion assembly, and intercellular movement. Previous sequence analysis of the TCV genome revealed the presence of five open reading frames which had the potential to encode gene products of 88, 38, 28, 9, and 8 kDa. Inoculation of protoplasts with infectious RNA revealed that only the p28 and p88 gene products are required for viral RNA synthesis. Although the p8 and p9 gene products were dispensable for RNA replication and virion assembly in protoplasts, mutations in the p8 and p9 genes prevented the production of systemic infections in plants. No viral RNA or protein was observed in the inoculated or systemic leaves of plants inoculated with transcripts synthesized from p8 or p9 mutant cDNAs. In contrast to these results, viral RNA was recovered from the inoculated, but not the systemic leaves, of plants inoculated with an RNA lacking the coat protein (CP) gene. With the CP mutant, no symptoms were observed on normally systemic hosts, but small local lesions were induced on Chenopodium amaranticolor. These results indicate that p8, p9, and CP are required for viral movement.
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