The transient coding transcript that carries genetic blueprints from chromosomal DNA in the nucleus to the ribosome for protein synthesis. Identified in 1961 by Sydney Brenner, François Jacob, and Matthew Meselson as the unstable intermediate linking phage genes to ribosomes, mRNA couples transcriptional control to cytoplasmic translation and now serves as a programmable therapeutic platform.
Encodes polypeptide amino-acid sequence in triplet codons read 5' to 3'
Clinical / Biotech Use
Nucleoside-modified mRNA vaccines, personalized cancer neoantigen vaccines, in vivo protein-replacement therapy
Structure & Biogenesis
Transcribed by RNA polymerase II from protein-coding genes as precursor messenger RNA (pre-mRNA) containing both coding exons and non-coding introns.
Co-transcriptionally modified at the 5' end with a 7-methylguanosine (m7G) cap linked via a 5'-to-5' triphosphate bridge, which shields the transcript from 5'-exonucleases and recruits the eIF4F initiation complex.
Introns are excised and exons are ligated in the nucleus by the spliceosome, a ribonucleoprotein machine built around five small nuclear RNAs; alternative splicing allows a single locus such as the calcitonin gene (CALCA) to yield distinct tissue-specific proteins.
Cleavage downstream of the polyadenylation signal (AAUAAA) is followed by addition of a 3' poly(A) tail of roughly 50 to 250 adenosine residues, governing nuclear export and cytoplasmic half-life.
Mechanism of Action
Mature mRNA is exported through nuclear pores into the cytoplasm, where the 40S subunit of the ribosome scans from the 5' cap across the 5' untranslated region (5' UTR) to locate the AUG start codon. The coding sequence (open reading frame) is decoded in non-overlapping three-nucleotide codons from 5' to 3' as aminoacyl-tRNA adaptors match each triplet and the ribosomal rRNA peptidyl transferase center forms peptide bonds until a stop codon (UAA, UAG, or UGA) recruits release factors.
Biological & Regulatory Roles
Transcript turnover ranges from minutes for immediate-early transcription factors and cytokines to many hours for structural and metabolic proteins, setting how quickly a cell can remodel its proteome.
The 3' untranslated region (3' UTR) harbors binding sites for microRNAs (such as let-7 and miR-21) and RNA-binding proteins (including FMRP encoded by FMR1), tuning translational efficiency and deadenylation-dependent decay.
Transcripts encoding secreted or transmembrane proteins carry a signal peptide that routes the translating ribosome to the rough endoplasmic reticulum via the signal recognition particle.
Degraded at the end of its functional lifespan by deadenylases, decapping enzymes, and intracellular ribonucleases, while quality-control pathways (nonsense-mediated decay) eliminate transcripts with premature stop codons.
Internal epitranscriptomic marks, most notably N6-methyladenosine (m6A) installed by methyltransferases, regulate mRNA splicing, export, and decay rates.
Therapeutic & Biotechnology Applications
In 2005, Katalin Karikó and Drew Weissman showed that incorporating modified nucleosides such as pseudouridine (or m5C, m6A, m5U, and s2U) into in vitro transcribed RNA largely abolishes its activation of Toll-like receptors TLR3, TLR7, and TLR8.
Encapsulated in ionizable lipid nanoparticles (LNPs), nucleoside-modified mRNA forms the basis of approved viral vaccines, investigational CRISPR-Cas9 editor delivery (encoding Cas9 mRNA alongside a guide RNA), and hepatic enzyme-replacement therapies.