Genome replication/expression strategies of positive-strand RNA viruses: a simple version of a combinatorial classification and prediction of new strategies.

A combinatorial approach to the classification of replication/expression strategies of positive-strand RNA virus genomes is suggested. Eighteen genome strategies defined as combinations of distinct modes of expression and replication are briefly characterized, 10 of which have been actually found in diverse virus groups. The chances for realization of the remaining eight strategies are evaluated. It is demonstrated that positive-strand RNA virus genome strategies are not necessarily monophyletic characters and could, in some cases, evolve convergently.