Heterologous RNA replication enhancer stimulates in vitro RNA synthesis and template-switching by the carmovirus, but not by the tombusvirus, RNA-dependent RNA polymerase: implication for modular evolution of RNA viruses.
Sequence comparisons reveal that positive-strand RNA viruses not only evolve by divergence from common ancestors but also by interviral recombination. A considerable number of these viruses, exemplified by the family Potyviridae, can in fact, be regarded as successful products of a number of recombination events. It is concluded that the recombinative character of RNA viruses will hamper any attempt to set up a true phylogenetic taxonomy. It is advisable, therefore, to avoid the introduction of any taxon higher-than-family in virus taxonomy.