Question

Suppose that you isolated an enveloped helical RNA virus. Purified RNA from this virus is capable of supporting translation in a rabbit reticulocyte cell-free translation system or in any other such system. Further analysis indicates that this virus replication is inhibited if infected cells are incubated with protease inhibitor such as trypsin inhibitor.

Based on this information, discuss the mechanism by which this virus replicates its genome in infected susceptible, permissive cells.

Answer 1

To multiply, a virus must first infect a cell. Susceptibility defines the capacity of a cell or animal to become infected. The host range of a virus defines both the kinds of tissue cells and the animal species which it can infect and in which it can multiply. Viruses differ considerably with respect to their host range. Some viruses (e.g. St. Louis encephalitis) have a wide host range whereas the host range of others (e.g. human papillomaviruses) may be a specific set of differentiated cells of one species (e.g human keratinocytes). In the course of infection, the virus introduces into the cell its genetic material — RNA or DNA — accompanied in many instances by essential proteins. The sizes, compositions, and gene organizations of viral genomes vary enormously. Viruses appear to have evolved by different routes and while no single pattern of replication has prevailed, two concepts are key to the understanding of how viruses multiply. First, the ability of a virus to multiply and the fate of an infected cell hinge on the synthesis and function of virus gene products — the proteins. Nowhere is the correlation between structure and function, between the sequence and arrangement of genetic material and the mechanism of expression of genes more apparent than in viruses. The diversity of mechanisms by which viruses ensure that their proteins are made is reflected but, unfortunately, not always deduced from their genomic structure. Second, although viruses differ considerably in the number of genes they contain, all viruses encode a minimum of three sets of functions which are expressed by the proteins they specify. Viral proteins