Interaction of mithramycin with isolated GC and CG sites

We have studied the interaction of the GC‐specific, minor groove‐binding ligand, mithramycin, with cloned DNA inserts containing isolated GC and CG sites flanked by regions of (AT)n and An · Tn using DNase I and hydroxyl radical footprinting. We find that mithramycin binds to GC better than CG and that AGCT is a better site than TGCA. Sites flanked by (AT)n appear to be bound better than those surrounded by An · Tn. Although no footprints are produced at T9GCA9 and T15CGA15, DNase I cleavage is enhanced with the GC sites suggesting that there is some interaction with the ligand. Mithramycin also alters the DNase I cleavage of (GA)n · (CT)n.