tRNA structure. A schematic of tRNA structure. tRNA is shown in its usual secondary structure, with colored circles representing nucleotides in and adjacent to the acceptor stem (pink), D stem–loop (green), anticodon stem–loop (red), variable arm (aqua) and T-stem–loop (gray), and lines representing base pairs. The 3′ CCA residues N74–N76 are shown in dark pink, and the anticodon residues N34–N36 are dark red. Outer disks of circles are colored to indicate common tertiary interactions, as first detailed for tRNAPhe from yeast (Kim et al. 1974b) (8–14, dark pink; 9–12–23, yellow; 13–22–46, red; 15–48, purple; 18–55, green; 19–56, blue; 26–44, light gray; 54–58, dark gray). Note that different tRNA species can have a D-stem with only 3 bp, a D-loop of variable length, a variable arm with 4 nt or a longer variable arm comprising a stem–loop. Note that tRNA residues are numbered so as to conserve constant numbering of major structural and functional elements, with the anticodon as N34–N36 and the CCA end as N74–N76 (Sprinzl et al. 1998). To this end, additional residues in the D-loop and variable arm have specialized names, and missing residues in some tRNA species are designated by gaps in the numbering for the appropriate residues. On the right is the corresponding crystal structure of tRNAPhe (1EHZ) (Shi and Moore 2000), with residues colored to match the schematic.
