(A) Domain organization of human XPB, color-coded as in Figure 3A. (B) Sequence alignments. Sequences used (species and UNIPROT or GENBANK accession code indicated): Human (Homo sapiens, P19447), mouse (Mus musculus, P49135), fruit fly (Drosophila melanogaster, Q02870), Choanoflagellate (Monosiga brevicollis, A9V0A0), fungus (Saccharomyces cerevisiae, Q00578), ciliate (Paramecium tetraurelia, XP_001448651.1), plant (Arabidopsis thaliana, Q38861), archaea (Ferroplasma, EQB73227.1, Thermoplasmatales, EQB71900.1), bacteria (Mycobacterium leprae, Q9CBE0) (Balasingham et al., 2012; Poterszman et al., 1997). Some archaeal XPBs, including the Archaeoglobus fulgidus homolog that served for structure determination (Fan et al., 2006), contain only the DRD, lacking the NTD/NTE, and were not included. Residues are numbered according to the human sequence. Identical residues are printed white on red background, similar residues in red on white background. Secondary structure elements, residues mutated in human disease (F99S, T119S), and the approx. 70-residue insertion in the DRD are indicated. Figure generated using the ESPript web server (Robert and Gouet, 2014).