Combinatorial rules of icosahedral capsid growth

A model of growth of icosahedral viral capsids is proposed. It takes into account the diversity of hexamers' compositions, leading to definite capsid size. We show that the observed yield of capsid production implies a very high level of self-organization of elementary building blocks. The exact number of different protein dimers composing hexamers is related to the size of a given capsid, labeled by its T-number. Simple rules determining these numbers for each value of T are deduced and certain consequences are discussed.