Figure 13:

The full proposed growth mechanism of VP1 pentamers to an incomplete or pseudo-closed template. The VP1 pentamer first contacts a stray C-terminal ligand of a VP1 pentamer already bound to the template. This binding can happen at large distances due to the length of the connector domains. If the capsid is incomplete, cooperative interactions can then bring the VP1 pentamer and the incomplete capsid together, and align them such that the final VP1 pentamer perfectly fits into the icosahedral hole on the template. This process is referred to as the elongation growth mechanism. If the capsid is pseudo-closed, the connected VP1 will have to allow the capsid to dynamically rearrange in order to add a VP1 pentamer to the capsid in a much slower process. The images at the bottom show what appears to be C-terminal ligand connections being made by free VP1 pentamers on pseudo-closed particles larger than T = 1 and smaller than T = 7 using electron microscopy,¹⁹ republished with permission of the Microibology Society, from Simian Virus 40 VP1 Capsid Protein Forms Polymorphic Assemblies In Vitro, Kanesashi et al., Journal of General Virology 2003, 84, 7, 2003; permission conveyed through Copyright Clearance Center, Inc. It should be noted that there is no template in this image and thus the VP1 pentamers are connected to the pseudo-closed capsid and to each other only by C-terminal ligand interactions.