Fig. 1. The structure of Tfi DNA ligase. (A) Domains and conserved sequence motifs of Tfi DNA ligase. Domains are in different colors: subdomain 1a, blue; subdomain 1b, cyan; domain 2, green; subdomain 3a, yellow; subdomain 3b, orange; domain 4, light pink. Residues in red are more strongly conserved than others. (B) Stereo ribbon diagram of Tfi DNA ligase. Drawn with MOLSCRIPT (Kraulis, 1991) and RASTER3D (Merritt and Bacon, 1997). Domain colors are the same as in (A). The covalently bound AMP moiety (stick model in purple) and a zinc ion (a cyan ball) are shown. Secondary structures were defined by PROCHECK (Laskowski et al., 1993). (C) Electron density map calculated using MAD solvent-flattened phases around the covalently bound AMP group. Atoms are yellow for carbon, red for oxygen, blue for nitrogen and cyan for phosphorus. (D) Residues around the AMP moiety. Atom colors are the same as above except black for carbon. Hydrogen bonds between the AMP and protein residues are represented by green dotted lines. Drawn with LIGPLOT (Wallace et al., 1995).