Figure 1. Crystal structures of EF-Tu, EF-Tu·aa-tRNA and EF-G. (a) Thermus aquaticus EF-Tu·GDP (protein data base (PDB) entry 1TUI, Polekhina et al., 1996). (b) The complex of T. aquaticus EF-Tu, GMPPNP (a GTP analogue) and yeast phenylalanyl-tRNA^Phe (PDB entry 1TTT; Nissen et al., 1995). (c) T. thermophilus EF-G·GDP (PDB entry 1DAR, al-Karadaghi et al., 1996). Proteins are portrayed as a tube representing the polypeptide backbone; effector nucleotides and aa-tRNA are shown as all-atom ball-and-stick. Structurally similar residues of the G domains (on which the structures are aligned) are coloured red, structurally similar residues of domains 2 are blue, the G¢ subdomain of EF-G is cyan, the G² insertion of EF-Tu is orange and the rest of the protein is grey. The guanine nucleotides bound to the G domains are yellow, as is the aa-tRNA, except that the amino acid of the tRNA is magenta and the three anticodon nucleotides are green. (Both figures were made with the program MidasPlus from the Computer Graphics Laboratory, University of California, San Francisco.)

Figure 2. Crystal structures of the complexes of EF-Tu and EF-Ts. (a) The complex in Escherichia coli (PDB entry 1EFU, Kawashima et al., 1996). (b) The complex in T. thermophilus (PDB entry 1AIP; Wang et al., 1997) showing the full heterotetramer. The structurally similar residues of the G domains of the two EF-Tu species (on which the structures are aligned) are red, the structurally similar residues of the domains 2 of EF-Tu are shown in blue, and the rest of the EF-Tu polypeptide is grey. The EF-Ts molecules are coloured pink (shaded differently to distinguish the EF-Ts monomers on the right), except that the identical and highly conserved amino acids are purple.