Proposed phylogenetic tree for the single-stranded RNA phages. The prototype combines infection and cell lysis in a single protein, A(L), and has a simple structure at the 3' end as SP and PP7. The branching off of the alloleviviruses partly relieves protein A(L) from its dual role by creating the read-through protein which helps in infection. In the leviviruses the A(L) protein is relieved from its lysis function by evolving the dedicated lysis protein. In coliphages GA and MS2 we observe the development of more and more elaborate 3' end structures. A similar tendency can be seen between SP or NL95 (species IV) and Q(beta), MX1 and M11 (species III).