What does it take to make a virus: The concept of the viral ‘self’

© 2010 by Imperial College Press. All rights reserved. Structural analyses now provide a framework to understand some aspects of virus evolution, where the three dimensional structures of virus capsids essentially substitutes for a fossil record. It has emerged that whilst many aspects of viruses are subject to horizontal gene transfer, for many viruses the core structures responsible for capsid assembly and genome packaging are highly conserved. We define this set of indispensable properties as the virus 'self'. A 'viral lineage' then comprises a set of viruses sharing a recognizably common 'self'. In this review we summarize the history and current status of the endeavour to develop a structure-based taxonomy based around this concept, highlighting not only some of the insights that this has brought, but also the problems that have emerged and the prospects for a systematic structure-based classification of the virosphere.