Spatial arrangement of the three alpha helices in the solution conformation of E. coli lac repressor DNA-binding domain.

The relative orientations of the 3 helices in the DNA-binding domain ('headpiece') of lac repressor have been determined using distance constraints obtained from 2-dimensional 1H nuclear Overhauser enhancement spectra. The relative orientations of its helices is similar to that of the central 3 helices in the DNA-binding domain of the lambda repressor of the bacteriophage lambda.