Fig. 1.

Molecular images illustrating the partition of a 182-bp DNA minicircle into equally sized, independent topological domains through the binding of the Lac repressor protein. Images rendered in PyMOL (http://www.pymol.org) with the DNA backbones depicted by tubes, the DNA bases by sticks, and the protein by ribbons. The DNA operators and the recognition headpieces on protein are highlighted in blue. The intervening segments of DNA are shown in different shades of gold and the remainder of the protein in green. Here, the operators attach in opposing antiparallel orientations to the binding headpieces of the protein