Heterogeneity of papillomaviruses.

The classification of the papillomaviral sequence into types is satisfactory for many purposes, but the resulting catalog does not accurately depict the extent of diversification of this family of viruses. Phylogenetic and mutational analyses reveal that some viral forms are much more ancient than other forms. Episodic evolutionary events and zoonotic transmission may have contributed to the overall pattern. Convergent evolution appears to be the best explanation for the scattered occurrence across the family tree of viruses with high oncogenic risk. We look for the determinants of this risk among the less conserved residues of the viral E6 and E7 transforming proteins.