An increasing number of structural studies are aimed at identifying the principles that govern protein-DNA recognition in gene regulation (1 ). This work depends on the successful reconstitution of protein-DNA complexes from their purified components. X-ray crystallography and two-dimensional NMR techniques require large amounts of pure protein and DNA. These can be supplied through expression in bacteria of the cDNA coding for intact proteins or their smaller DNA-binding domains and the automated chemical synthesis of DNA in the laboratory.