Many viruses make us sick, so of course it is a good idea to find out how they work in order to stop them; in addition, however, scientists have found that the simplicity of viruses' method of replication make them excellent models for exploring the basic mechanics of gene expression and regulation.

Viruses, being obligatory parasites of their host cells, rely on a vast supply of cellular components for their replication, regardless of whether infection leads to cell death or to the state of persistence. Animal viruses are providing scientists with relatively simple models to study the molecular biology of genome replication and gene expression. Whereas viruses use, in general, pathways of macromolecular biosynthesis common to the host cell, they have a cunning ability to adopt unusual mechanisms of gene expression and gene replication, provided these special pathways offer an advantage...