Virtuelle (Nano) Welten: PDB Molecule of the Month 15: tRNA

Transfer RNA Structure

Transfer RNA molecules are composed of one short chain of RNA, 70-90 nucleotides in length, folded into a trefoil shape. Two different molecules are shown here, phenylalanine tRNA (PDB entry 4tna) and aspartate tRNA (PDB entry 2tra). The two ends of the RNA chain are close to one another at the pointed end of the L-shaped structure, at the top in this illustration. The amino acid is added here, at the position shown by the arrows. The center of the chain forms the rounded leg of the L, shown here at the bottom, exposing the three nucleotides that form the anticodon. The other two loops of the trefoil are bundled into the elbow, where they provide structure to the whole molecule. The four normal RNA bases-adenine, uracil, guanine and cytosine-- obviously do not provide enough latitude to form a sturdy structure, because many of the bases are modified to enhance their structures. To see two particularly exotic examples, look at the base next to the anticodon, number 37, in the initiator methionine tRNA (PDB entry 1yfg) or the phenylalanine tRNA (PDB entries 4tna and 6tna).