Laboratory evolution of virus-like nucleocapsids from nonviral protein cages

Abstract

Significance Viruses consist of a protective proteinaceous shell that packages a DNA or RNA genome. The critical step in the evolution of primitive viruses was presumably the emergence of protein cages that could load, protect, and transfer their own genetic information. Here, we show that a nonviral protein cage formed by Aquifex aeolicus lumazine synthase and its encoding mRNA can be engineered and evolved into virus-like nucleocapsids. The optimized proteins specifically recognize designed motifs on cognate mRNAs, and these RNA tags can also be employed for the encapsulation of other RNA molecules. These model systems have great potential for the investigation of nucleocapsid assembly and evolution and as tailored protein compartments for protective packaging and delivery of nucleic acids.