The crystal structure of a putative transcriptional regulator protein TM 1030 from Thermotoga maritima, a hyperthermophilic bacterium, was determined by an unusual multi-wavelength anomalous dispersion method at 2.0 angstrom resolution, in which data from two different crystals and two different beamlines were used. The protein belongs to the tetracycline repressor TetR superfamily. The three-dimensional structure of TM1030 is similar to the structures of proteins that function as multidrug-binding transcriptional repressors, and contains a large solvent-exposed pocket similar to the drug-binding pockets present in those repressors. The asymmetric unit in the crystal structure contains a single protein chain and the twofold symmetry of the dimer is adopted by the crystal symmetry. The structure described in this paper is an apo- form of TM1030. Although it is known that the protein is significantly overexpressed during heat shock, its detailed function cannot be yet explained. (c) 2007 Elsevier Inc. All rights reserved.