the antibiotic distamycin, which binds in the minor groove of DNA segments that have specifi c sequences (Figure 2.22B and C). Up to two molecules of distamycin can bind side by side in a single region of the minor groove, but the minor groove has to expand considerably in order to accommo- date two distamycin molecules. Since both types of complex can form at the same DNA sequence, with similar binding energetics, the change in groove width must be a fairly low-energy process