mRNA Display is an in vitro selection and directed-evolution technology that physically couples a peptide (or protein) to the mRNA sequence that encodes it through a covalent bond. This genotype–phenotype “fusion” allows researchers to screen enormous molecular libraries and then recover the winning sequences by amplification, enabling fast, iterative optimization under tightly controlled experimental conditions. 1) The Core Idea: Genotype–Phenotype Coupling Without Cells Every selection technology needs a reliable way to keep “what a molecule does” attached to “the information that made it.” In mRNA Display, that attachment is literal: the newly made peptide becomes covalently linked to its own mRNA, producing a stable fusion that survives stringent washing and enrichment steps. This is a major conceptual advantage over systems where the linkage is non-covalent or depends on living cells for propagation. Because the entire workflow is performed in vitro, the experimenter can tune conditions (buffers, salts, temperature, denaturants, competitors) to match the target biology and the selection pressure they want to apply. 2) How the Covalent Link Is Formed: Puromycin at the 3′ End The “magic” reagent behind classic mRNA Display is puromycin, a molecule that mimics the 3′ end of an aminoacyl-tRNA. When puromycin is physically…
