Résumé:

We develop methods based on theory of representations of continuous and discrete groups; theory of invariants for the groups not-generated by reflections; and theory of bifurcations of invariants functionals. It is applied to the protein arrangement in Satellite Tobacco Mosaic virus, Cowpea Chlorotic Mottle virus and Sindbis virus (which verify Caspar and Klug selection rules) and in L-A virus, Dengue virus and Murine Polyoma virus (which violate Caspar and Klug rules).