Tobacco mosaic virus and the study of early events in virus infections

In order to establish infections, viruses must be delivered to the cells of potential hosts and must then engage in activities that enable their genom es to be expressed and replicated. With most viruses, the events that prece de the onset of production of progeny virus particles are referred to as th e early events and, in the case of positive-strand RNA viruses, they includ e the initial interaction with and entry of host cells and the release (unc oating) of the genome from the virus particles. Though the early events rem ain one of the more poorly understood areas of plant virology, the virus wi th which most of the relevant research has been performed is tobacco mosaic virus (TMV). In spite of this effort, there remains much uncertainty about the form or constituent of the virus that actually enters the initially in vaded cell in a plant and about the mechanism(s) that trigger the subsequen t uncoating (virion disassembly) reactions. A variety of approaches have be en used in attempts to determine the fate of TMV particles that are involve d in the establishment of an infection and these are briefly described in t his review. In some recent work, it has been proposed that the uncoating pr ocess involves the bidirectional release of coat protein subunits from the viral RNA and that these activities may be mediated by cotranslational and coreplicational disassembly mechanisms.