Polyoma viruses. Coloured scanning electron micrograph (SEM) of polyoma viruses, members of the papovirus family. The viruses consist of an icosahedral protein capsid (coat, green) that encloses the genetic material, DNA (deoxyribonucleic acid, orange). The genetic material of papoviruses is unique amongst viruses as the DNA forms a circular molecule instead of the usual strands. There are a number of polyoma viruses, many are asymptomatic, but same do cause disease, such as the BK virus that causes respiratory illness in children. Magnification: x115500 when printed 10 centimetres wide.