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Fig. 1. Schematic drawing of the structure of T. thermophilus IleRS. The NH2-terminal extension, the Rossmann-fold domain, an ƒÑ-ƒÑ-ƒÒ-ƒÑ domain specific to monomeric class I synthetases (31), and the -helix bundle domain are shown in white, orange, violet, and red, respectively. The COOH-terminal 217 residues of the IleRS are partially disordered, and only two helices (shown in pink) could be traced. In addition, the IleRS has an insert, in the Rossmann-fold domain, consisting of four structural domains (Ins-1, Ins-2, Ins-3, and Ins-4 domains, as shown in blue, aqua, green, and light green, respectively). The bound Zn2+ ions are represented by red balls.