Background Overview

Traditional phage display and yeast display technologies are constrained by transformation efficiency, typically yielding libraries of 10⁹–10¹⁰ variants. mRNA display technology breaks this bottleneck by in vitro translation of genotype-phenotype linked molecules, enabling trillion-scale (10¹²–10¹⁴) peptide libraries for antibody discovery, enzyme directed evolution, and protein-protein interaction mapping. Hzymes provides high-fidelity T7 RNA polymerase, modified nucleotides (N1-Me-pUTP, Pseudo UTP), and optimized IVT reagents specifically formulated for mRNA display library construction, ensuring high yield, low dsRNA, and sequence fidelity.

mRNA Display

mRNA display is an in vitro selection and directed evolution technique that can screen trillions of mRNA–protein fusion variants in a single experiment to achieve desired functions. In directed evolution, to alter the binding or catalytic properties of target proteins or peptides, a combination of in vitro and in vivo techniques can be employed to isolate proteins with the intended function from vast variant mixtures.

Figure 1. In vitro screening workflow via mRNA display

01 Constructing the DNA Library Encoding mRNA

A large random DNA library is constructed to encode mRNA, with specific modifications applied: adding a transcription promoter (e.g., T7 promoter), translation enhancer, start codon, and other elements at the 5' end; an open reading frame (ORF) containing a mix of fixed and random codons, designed according to the target protein; omission of a stop codon at the 3' end; and the addition of affinity purification tags.

02 RNA Transcription and Coupling with Puromycin

In vitro, RNA polymerase transcribes the DNA into mRNA, after which the 3' end of the mRNA is ligated to a nucleic acid fragment containing puromycin.

03 In Vitro Translation to Form mRNA–Peptide Complexes

Ribosomes use puromycin-linked mRNA as a template for translation, generating nascent peptides. Puromycin enters the ribosome A site, where the C-terminal of the peptide chain forms an amide bond with puromycin’s amino group, terminating translation. This results in a stable mRNA–peptide fusion, which can then be purified from ribosomes and other reaction components.

Figure 2. Various DNA library designs and incorporation of non-natural amino acids for constructing diverse peptide libraries

04 Reverse Transcription to Form cDNA/mRNA–Peptide Complexes

Reverse transcription-PCR (RT-PCR) is used to convert the mRNA into complementary DNA (cDNA). This produces a cDNA/mRNA–peptide fusion complex, stabilizing the nucleic acid component and accelerating recovery of genetic information after screening.

05 Screening and Separation

Using ELISA, magnetic beads, or similar methods, the target is immobilized on a solid support. cDNA/mRNA–protein fusions that bind specifically to the target are retained, while non-binding fusions are removed.

06 Amplification to Obtain the Next-Round DNA Template

At high pH, the mRNA is hydrolyzed from the cDNA/mRNA–protein fusions, releasing cDNA. This cDNA is amplified via PCR, providing templates for the next round of screening or sequencing. Error-prone PCR can be applied at this stage to increase sequence diversity.

07 Enrichment of Target Proteins and Gene Sequences

Through the diversity of the DNA library and repeated target interactions, 4–10 rounds of screening enrich peptide sequences with high target-binding affinity. Sequencing the cDNA identifies the peptide structures.

Why is Puromycin the “Essential Component” of mRNA Display?

The core of mRNA display technology lies in achieving precise coupling between genotype (mRNA) and phenotype (protein). Puromycin serves as the indispensable “molecular bridge” for this process.

As an aminoacyl-tRNA analog, puromycin has a unique chemical structure: it can be recognized by the ribosome and participate in peptide chain elongation, while also forming a stable amide bond with the nascent peptide chain during translation. When puromycin is attached to the 3' end of mRNA, the ribosome mistakenly incorporates it as an “amino acid,” allowing it to enter the ribosome A site. Catalyzed by the peptidyl transferase center (PTC), its free amino group accepts the nascent peptide from the P-site tRNA, incorporating it into the chain (Figure 3). Because the peptide bond between puromycin’s structural components cannot be cleaved by aa-tRNA, the result is a stable covalent linkage of mRNA and protein — essentially a “hook” that firmly locks the translation product to its encoding mRNA.

Figure 3. Schematic of puromycin-mediated mRNA–peptide fusion formation
(Puromycin is a structural mimic of the aminoacylated 3' terminus of tRNA. Differences from tyrosine-tRNA are highlighted in red.)

Development of Puromycin Linkers

Attaching puromycin to the 3' end of mRNA requires careful design and operation. To improve the efficiency of puromycin–mRNA coupling, linker strategies have been gradually refined (Figure 4).

Figure 4. Comparison of methods for preparing mRNA–puromycin linkers

01 Splint DNA

In the earliest form of mRNA display, splint DNA was used with T4 DNA/RNA ligase to join mRNA and puromycin linkers. Despite using a >200-fold molar excess of puromycin linker, the ligation efficiency remained very low.

02 Long Biotinylated Puromycin Linker (LBP)

To address low ligation efficiency and mRNA instability, LBP was developed by incorporating hybridization regions complementary to mRNA and biotin. This enabled a cDNA display variant, as the linker itself contained a reverse transcription primer region, eliminating the need for an additional primer. Hybridization between the linker and mRNA improved ligation efficiency via T4 RNA ligase. Biotin facilitated immobilization of mRNA display molecules on magnetic beads for easy washing, removal of ribosomes and other contaminants, and preparation for reverse transcription. Biotin could then be removed using restriction enzyme sites within LBP.

03 Short Biotinylated Puromycin Linker (SBP)

A shorter linker sequence reduced DNA synthesis costs while improving mRNA–linker ligation efficiency. RNase T1 was used to cleave biotin specifically at guanosine residues in single-stranded RNA.

04 cnvK Puromycin Linker via Photo-Crosslinking

Incorporating the cnvK base reduced mRNA degradation by eliminating the need for T4 RNA ligase buffer containing cationic activators that trigger RNase contamination. Photo-crosslinking between mRNA and the cnvK-puromycin linker occurred at a ratio of 1:1–1.5, requiring only about one minute.

mRNA Display Screening Case Studies

With its vast library capacity, tunable screening control, and shorter experimental cycles, mRNA display has become a rising platform for peptide drug discovery.

For instance, MK-0616 was identified using Ra Pharmaceuticals’ mRNA display cyclic peptide library. After over two years of medicinal chemistry optimization, the initial 12-amino acid monocyclic peptide was refined into an 8-amino acid tricyclic peptide.

On June 9, 2025, Merck announced that its oral PCSK9 inhibitor enlicitide decanoate (MK-0616) achieved primary endpoints in two pivotal Phase III trials for hypercholesterolemia. This milestone suggests it could become the world’s first oral PCSK9 inhibitor, offering a new potential therapy for lowering LDL-C.

Another drug, zilucoplan, also developed by Ra using mRNA display technology, was approved by the U.S. FDA in October 2023 for treating myasthenia gravis.

Conclusion

In summary, mRNA display technology, with its vast mutant library capacity, precise genotype–phenotype coupling, and highly flexible screening strategies, has become a critical platform in modern protein engineering and drug development. Puromycin plays an irreplaceable role as the “molecular bridge,” enabling efficient correspondence between genes and proteins while greatly improving screening efficiency and accuracy. With continued advancements in puromycin linker technologies, mRNA display systems have significantly improved in expression efficiency, stability, and versatility. In recent years, this platform has driven the emergence of innovative peptide and protein drugs, accelerating their development. Looking ahead, ongoing technical optimizations will further expand the potential of mRNA display for drug discovery, protein interaction research, and the broader biopharmaceutical industry.

Hzymes and mRNA Display

Hzymes Life Science Solutions

Hzymes offers a comprehensive range of products for molecular biology, cell biology, and synthetic biology. These include nucleic acid extraction, molecular cloning, cell culture, cell transfection, cryopreservation, cell assays and sorting, complete raw materials for RNA synthesis, and cell-free in vitro protein synthesis products. In addition, Hzymes provides DNA synthesis, RNA synthesis, and recombinant protein CDMO services.

Bibliography

[1] Kamalinia G, Grindel B J, Takahashi T T, Millward S W and Roberts R W 2021 Directing evolution of novel ligands by mRNA display Chem. Soc. Rev. 50 9055–103

[2] Arai H, Kumachi S and Nemoto N 2019 cDNA Display: A Stable and Simple Genotype–Phenotype Coupling Using a Cell-Free Translation System (Springer US)[3] Kamalinia G, Grindel B J, Takahashi T T, Millward S W and Roberts R W 2021 Directing evolution of novel ligands by mRNA display Chem. Soc. Rev. 50 9055–103[4] Peacock H and Suga H 2021 Discovery of De Novo Macrocyclic Peptides by Messenger RNA Display Trends in Pharmacological Sciences 42 385–97