Quasispecies as a matter of fact: Viruses and beyond

We review the origins of the quasispecies concept and its relevance for RNA virus evolution, viral pathogenesis and antiviral treatment strategies. We emphasize a critical point of quasispecies that refers to genome collectivities as the unit of selection, and establish parallels between RNA viruses and some cellular systems such as bacteria and tumor cells. We refer also to tantalizing new observations that suggest quasispecies behavior in prions, perhaps as a result of the same quantum-mechanical indeterminations that underlie protein conformation and error-prone replication in genetic systems. If substantiated, these observations with prions could lead to new research on the structure–function relationship of non-nucleic acid biological molecules.

► Mutant spectra act as interacting sets of variant viruses subjected to group selection.
► The target of selection may be realized through complementing or interfering interactions.
► Cooperative interactions can modulate virulence in bacteria.
► Cellular heterogeneity lies at the basis of tumor progression.
► Prions become heterogeneous by accumulating protein-folding mutants.