The strategies of plant virus gene expression: models of economy

Given the small size of their genome, the genetic information of viruses is extremely compact, and non-coding regions are very limited as compared to those of prokaryotic and eukaryotic cell systems. Viruses utilize cell components at all levels of the replication cycle for their own benefit, not the least being the translation machinery. They have also evolved a number of highly sophisticated strategies to produce and regulate the production of the proteins required for their propagation. In addition, these proteins are often multifunctional, encoding several essential virus-specific proteins. At the level of transcription, these strategies include splicing, the production of subgenomic RNAs from virus templates and cap-snatching. At the level of translation, regulation exists at all steps: initiation, elongation and termination. Furthermore, viruses frequently resort to co- and/or post-translational cleavage of a polyprotein precursor to yield the mature proteins.