display technology mrna display MI:0073 PSI-MI This method relies on the covalent coupling of mRNA to the nascent polypeptide. The mRNA (natural or artificial) is first covalently linked to a short DNA linker carrying a puromycin moiety. The mRNA mixture is then translated in vitro. When the ribosome reaches the RNA-DNA junction the ribosome stalls and the puromycin moiety enters the peptidyltransferase site of the ribosome and forms a covalent linkage to the nascent polypeptide. As a result the protein and the mRNA are covalently joined and can be isolated from the ribosome and purified. In the current protocol, a cDNA strand is then synthesised to form a less sticky RNA-DNA hybrid and these complexes are finally used for affinity selection. As in most display approaches, several selections cycles (3-6) are sufficient to enrich for mRNAs encoding ligand proteins.