Figure 2

a | Structure of the 160S poliovirus particle. Reproduced with permission from Ref. 106 © (2000) American Society for Microbiology. b | Surface topology of adeno-associated virus 2. The protruding spikes are coloured white. Reproduced with permission from Ref. 105 © (2002) National Academies of Sciences, USA. c | Structure of Semliki Forest virus. The colour scheme reflects the radial distance from the centre of the virion, increasing from blue to red. Reproduced with permission from Ref. 23 © (2000) Elsevier Science. d | Structure of the severe acute respiratory syndrome (SARS) coronavirus. The coronavirus particle has club-shaped surface projections — known as spikes. Adeno-associated virus 2 and Semliki Forest virus particles (not to scale) are comparable in size to Poliovirus. Reproduced with permission from Ref. 107 © (2003) Massachusetts Medical Society.