The microviridae: Diversity, assembly, and experimental evolution

The Microviridae, comprised of ssDNA, icosahedral bacteriophages, are a model system for studying morphogenesis and the evolution of assembly. Historically limited to the phi X174-like viruses, recent results demonstrate that this richly diverse family is broadly divided into two groups. The defining feature appears to be whether one or two scaffolding proteins are required for assembly. The single scaffolding systems contain an internal scaffolding protein, similar to many dsDNA viruses, and have a more complex coat protein fold. The two-scaffolding protein systems (phi X174-like) encode an internal and external species, as well as an additional structural protein: a spike on the icosahedral vertices. Here, we discuss recent in silica and in vivo evolutionary analyses conducted with chimeric viruses and/or chimeric proteins. The results suggest 1) how double scaffolding systems can evolve into single and triple scaffolding systems; and 2) how assembly is the critical factor governing adaptation and the maintenance of species boundaries. (C) 2016 Elsevier Inc. All rights reserved.