This family consists of various adenovirus penton base proteins, from both the Mastadenoviradae having mammalian hosts and the Aviadenoviradae having avian hosts. The penton base is a major structural protein forming part of the penton which consists of a base and a fibre, the pentons hold a morphologically prominent position at the vertex capsomer in the adenovirus particle. In mammalian adenovirus there is only one tail on each base where as in avian adenovirus there are two.