The Bromoviruses

Abstract

Brome mosaic virus (BMV), broad bean mottle virus (BBMV), and cowpea chlorotic mottle virus (CCMV) are collectively known as the bromoviruses. Although these plant viruses differ widely in their host ranges, they are all spherical with anhydrous diameters of about 25 nm; they all contain about a million daltons of RNA and 180 protein subunits weighing about 20,000 daltons each. The bromoviruses are particularly suited to the studies of virus structure and of plant virus replication. They are stable, easily isolated in gram quantities, and they are the only spherical viruses that can be easily and efficiently reassembled from protein and RNA. Their genomes, which consist of three independently encapsidated RNA components, are amenable to crude genetic analysis. Brome mosaic virus RNA is an efficient messenger in a wheat embryo protein synthesizing system. Cowpea chlorotic mottle virus infects the tobacco protoplasts efficiently and synchronously. The basic tools are now available for studying the bromovirus replication at the molecular level. This chapter approaches the bromoviruses as a molecular biologist. After briefly introducing the virus, it proceeds from the simplest molecular aspects of the virus, the structure of its protein and RNA, to the virus itself and finally, to the more complex biological properties of the virus.