Papillomaviruses and Polyomaviruses are composed solely of pentameric capsomeres for a total of 360 capsid proteins. Nevertheless their icosahedral structure is that of a T=7 capsid in which pentamers occupy hexavalent positions.
Icosahedric triangulation number is calculated following Caspar and Klug system
Physical principles in the construction of regular viruses
D. L. Caspar, A. Klug
Cold Spring Harb. Symp. Quant. Biol. 1962; 27: 1?24
D. L. Caspar, A. Klug
Cold Spring Harb. Symp. Quant. Biol. 1962; 27: 1?24