In: Encyclopedia of Life Sciences (eLS). John Wiley & Sons, Ltd: Chichester. DOI: 10.1002/9780470015902.a0023265
Evolution of viruses is considerably more rapid than that of the cellular organisms that they infect. The reach of sequence-based evolutionary studies on viruses is therefore rather limited. The tertiary protein structure is generally conserved over longer time periods than the primary one. Indeed, structural studies proved to be more informative for reconstructing deep evolutionary connections between distantly related viruses. It has become apparent that certain viruses infecting hosts from different domains of life are remarkably similar in their virion
assembly and architecture, suggesting a common ancestry for these structurally related viruses. Furthermore, the presence of several distinct architectural principles employed by viruses suggested that the origin of the current virosphere has multiple evolutionary origins. Insights obtained from numerous structural studies may not only be successfully used to refine the existing virus classification scheme, but may also lead to a major shift in our understanding on the origin, evolution and organisation of the viral domain.