Cucumber Mosaic Virus Replication in Cowpea Protoplasts: Time Course of Virus, Coat Protein and RNA Synthesis

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Abstract
The time course of the synthesis of cucumber mosaic virus (CMV), CMV coat protein and the four CMV RNAs has been followed in cowpea protoplasts. CMV synthesis was estimated by analytical sucrose gradient centrifugation of extracts from protoplasts and by infectivity assay; coat protein synthesis was determined by incorporation of radioactive amino acids and analytical polyacryl-amide slab gel electrophoresis, while the synthesis of CMV RNAs was determined by hybridization analysis with labelled specific complementary DNA (cDNA) probes. There was a co-ordinate synthesis of CMV, CMV coat protein and virus RNA up to 50 h p.i. whereas the rate of coat protein synthesis reached a peak at about 15 h p.i. Coat protein was the only virus-induced protein detected. Results on the relative synthesis of RNAs 3 and 4 indicated that RNA 4 was derived by nucleolytic cleavage of RNA 3 and not by transcription of a negative RNA 4 strand.