SUNY at Albany
June 19-23, 2001
Actinomycin D Binds Strongly to d(TGTCATG) with a 2:1 Drug to DNA Duplex Binding Stoichiometry
Recent finding from our laboratory indicated that actinomycin D (ACTD) binds strongly to d(TGTCATTG), an apparent single-stranded DNA devoid of the drug-preferred GpC site. A hairpin binding model was speculated for such a binding, involving a fold-back G¥C base pair formation and the stacking of the 3'-sides of both G's on the opposite faces of the drug chromophore with swing-out T base. However, it was also suggested that an off-registered duplex binding with similar binding principles could also be operative at higher DNA concentrations. To support such a contention, ACTD binding studies are hereby carried out with d(TGTCATG). This heptamer differs from the parent octamer d(TGTCATTG) by a mere removal of a T base to result in concomitant reduction and enhancement of monomeric hairpin and dimeric duplex formation, respectively. It was found that ACTD binds well to d(TGTCATG) with 1 drug to 1 strand (or 2 drugs to one duplex) binding stoichiometry. These results are consistent with a model in which a dimeric duplex is formed at the self-complementary -CATG- tetranucleotide sequence with TGT dangling ends and the two drugs are bound at both ends of the duplex with the 3'-sides of the dangling G bases stacking on the other faces of the drug chromophores with swing-out T bases. Results on related oligomers will also be presented to support such a duplex binding model.
Fu-Ming Chen and Feng Sha
Department of Chemistry, Tennessee State University, Nashville, Tennessee 37209-1561