The physical adaptor molecule of the genetic code, matching three-nucleotide codons on messenger RNA to their corresponding amino acids inside the ribosome. In 1965, Robert W. Holley and colleagues determined the 77-nucleotide sequence and cloverleaf secondary structure of yeast alanine tRNA — the first complete nucleotide sequence of any nucleic acid.
Delivers esterified amino acids to the ribosomal decoding and peptidyl transferase centers
Clinical / Biotech Use
Engineered suppressor tRNAs for nonsense-mutation readthrough and non-canonical amino-acid incorporation
Structure & Biogenesis
Transcribed in the nucleus by RNA polymerase III from hundreds of dispersed nuclear tRNA genes, alongside 22 distinct tRNAs encoded directly by the circular genome of the mitochondrion.
Pre-tRNA transcripts undergo 5' leader cleavage by the catalytic RNA subunit of RNase P, 3' trailer trimming, enzymatic addition of an invariant 3'-CCA trinucleotide tail, and extensive post-transcriptional base modification (pseudouridine, dihydrouridine, inosine, and methylations guided in part by snoRNAs).
Folds into a four-arm cloverleaf secondary structure (acceptor stem, D-arm, anticodon arm, and TΨC arm) that coaxially stacks into an L-shaped three-dimensional tertiary structure stabilized by tertiary hydrogen bonds and magnesium ions.
Mechanism of Action
Each tRNA is charged at its 3'-CCA adenosine ribose hydroxyl (2'-OH or 3'-OH) with its cognate amino acid by a dedicated aminoacyl-tRNA synthetase, an ATP-dependent class 6 ligase that forms an aminoacyl-AMP intermediate and proofreads misactivated substrates. Delivered to the ribosome A-site by GTP-bound elongation factor eEF1A, the tRNA anticodon loop base-pairs antiparallel to the mRNA codon; accurate geometry triggers GTP hydrolysis and positions the aminoacyl stem in the rRNA peptidyl transferase center for peptide bond transfer.
Biological & Regulatory Roles
Wobble base-pairing at the first anticodon position (position 34, often modified to inosine) allows a repertoire of roughly 45 to 50 human tRNA anticodon isoacceptors to decode all 61 sense codons.
A specialized initiator methionyl-tRNA (tRNAiMet) binds initiation factor eIF2 to recognize the AUG start codon directly in the ribosomal P-site, distinct from elongator methionyl-tRNA.
Under cellular stress, angiogenin (an RNase A superfamily enzyme) cleaves mature tRNAs within the anticodon loop to generate tRNA-derived stress-induced fragments (tiRNAs and tRFs) that inhibit global translation initiation.
Interactions & Complexes
Cycles sequentially through the A (aminoacyl), P (peptidyl), and E (exit) sites formed at the interface of the 40S and 60S ribosomal subunits during protein elongation.
Uncharged tRNAs accumulating during amino-acid starvation bind and activate the kinase GCN2, phosphorylating eIF2α to couple nutrient availability to translational control.
Therapeutic & Biotechnology Applications
Pathogenic mutations in mitochondrial tRNA genes cause multisystem oxidative phosphorylation disorders, including MELAS (MT-TL1 A3243G) and MERRF (MT-TK), while cytoplasmic aminoacyl-tRNA synthetase mutations cause Charcot-Marie-Tooth peripheral neuropathies.
Engineered anticodon-edited suppressor tRNAs are in preclinical and clinical development to read through premature termination codons (UGA, UAG, UAA) and restore full-length protein synthesis in genetic diseases.