tRNA

Transfer RNA (tRNA) is a small RNA molecule that acts as the adaptor between messenger RNA codons and amino acids during protein synthesis. Each tRNA carries a specific amino acid and contains an anticodon that base-pairs with a complementary codon on the mRNA, guiding the incorporation of the amino acid into the growing polypeptide.

Most mature tRNAs are about 70–90 nucleotides long and fold into a cloverleaf secondary structure with four arms: the acceptor stem bearing the 3' CCA aminoacylation site, the D loop, the anticodon loop, and the TΨC loop. In three-dimensional space, tRNA adopts an L-shaped conformation that positions the amino acid and anticodon for interaction with the ribosome. The 3' CCA tail is the attachment point for amino acids, and its presence is sometimes encoded in the gene and sometimes added post-transcriptionally by tRNA nucleotidyltransferase.

Amino acids are attached to tRNAs by aminoacyl-tRNA synthetases, a family of enzymes that ensure each tRNA is charged with the correct amino acid using ATP. The charged tRNA then participates in translation at the ribosome, where codon-anticodon recognition occurs with assistance from translation factors. Wobble base pairing at the third codon position allows some tRNAs to recognize multiple codons for the same amino acid, increasing decoding efficiency.

tRNA genes are diverse and widespread across all domains of life, producing multiple isoacceptors and isodecoders. They undergo extensive post-transcriptional modifications that influence structure and decoding accuracy. In addition to their canonical role, tRNA-derived fragments have been observed in various cellular contexts.