The solution structure of the N-terminal zinc binding domain (residues 1-55; IN1-55) of HIV-1 integrase has been solved by NMR spectroscopy. IN1-55 is dimeric, and each monomer comprises four helices with the zinc tetrahedrally coordinated to His 12, His 16, Cys 40 and Cys 43. IN1-55 exists in two interconverting conformational states that differ with regard to the coordination of the two histidine side chains to zinc. The different histidine arrangements are associated with large conformational differences in the polypeptide backbone (residues 9-18) around the coordinating histidines. The dimer interface is predominantly hydrophobic and is formed by the packing of the N-terminal end of helix 1, and helices 3 and 4. The monomer fold is remarkably similar to that of a number of helical DNA binding proteins containing a helix-turn-helix (HTH) motif with helices 2 and 3 of IN1-55 corresponding to the HTH motif. In contrast to the DNA binding proteins where the second helix of the HTH motif is employed for DNA recognition, IN1-55 uses this helix for dimerization.