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Publisher Summary This chapter presents the structure and properties (physical, chemical, and biological) of the tobacco mosaic virus (TMV). TMV is a rod-shaped particle. The virus particle is built up of a helical array of subunits set about the long axis of the particle. The protein subunits of the TMV are packed together in such a way as to leave space for the RNA between them. Thus, the RNA is embedded tightly between protein subunits. The self assembly of protein subunits to form a helical structure similar to that of TMV can take place with or without RNA. However, the association of RNA contributes to the stability of the completed particle. The chapter also discusses the events that take place within the host cell following infection with TMV. TMV is composed of 95% protein and 5% RNA. This RNA is released into the host cell to initiate infection. The parental viral RNA may remain bound to the nuclear structures in the host cell and does not enter the pool of newly synthesized viral RNA (progeny viral RNA), which is rapidly assembled into the progeny TMV. The parental RNA localized in the nucleus performs dual functions: one is that of a messenger directing the synthesis of the needed enzymes and the other is that of a template in the synthesis of its complementary strand.

THE mode of replication of RNA or RNA-containing tumour viruses is not understood. The recent studies on Rous sarcoma and other RNA-containing oncogenic viruses suggest that the replicative cycle of the RNA of these viruses might not be associated with ribonuclease-resistant structures (double stranded RNAs), but might involve the synthesis of a DNA intermediate specific to viral RNA1–3. Two groups of workers, however, presented evidence for the presence of a double stranded RNA in 78 Al cell line of rat embryo fibroblasts which had been transformed and chronically infected with the murine sarcoma-leukaemia virus complex (MSV-MLV)4,5 and it was suggested that the mode of replication of oncogenic viral RNAs was the same as that of non-oncogenic viral RNAs4. This apparent discrepancy prompted me to look for ribonuclease-resistant RNA structures in the chick embryo cells transformed by Schmidt-Ruppin Rous sarcoma virus (SR-RSV).