Non-quasi-equivalent configurations can also be predicted. The viral capsid of SV40 contains 360 identical coat protein subunits arranged as 72 pentamers, an example of a non-quasi-equivalent capsid organization. (a) The outermost constraints (magenta) are grouped around the 12 clusters of five proteins (pentamers) at the particle fivefold axes of icosahedral symmetry. (b) Cross-sectional view of the capsid, showing the locations of points in the array relative to protein. (c)–(g) Ribbon representations of the two different types of pentamers in the capsid; (c), (d) top and side view of the 12 pentamers at the fivefold axes, viewed from outside the capsid; (e), (f) show the corresponding views for the 60 pentamers off the symmetry axes; (g) shows both pentamer environments simultaneously as situated in the capsid. The new geometric principle of virus architecture distinguishes between the two types of pentamer environments and incorporates this viral geometry that cannot be modelled in quasi-equivalence theory.