In vitro virus: Bonding of mRNA bearing puromycin at the 3′‐terminal end to the C‐terminal end of its encoded protein on the ribosome in vitro

Adequate means for genotype assignment to phenotype is essential in evolutionary molecular engineering. In this study, construction of ‘in vitro virus’ was carried out in which a genotype molecule (mRNA) covalently binds to the phenotype molecule (protein) through puromycin on the ribosome in a cell‐free translation system. Bonding efficiency was ∼10%, thus indicating a population of the in vitro virus to have ∼10 12 protein variants, this number being 10 4 that in the phage display. The in vitro virus is useful for examining protein evolution in a test tube and the results may possibly serve as basis for a general method for selecting proteins possessing the most desirable functions.