The DNA base sequence of the lactose operator and the base changes associated with eight OC mutations. Regions of twofold rotational symmetry are indicated by color and by a dot at their axis of symmetry.
[Data from W. Gilbert, A. Maxam, and A. Mirzabekov, in N. O. Kjeldgaard and O. Mall0e, eds., Control of Ribosome Synthesis. Academic Press, 1976]