Actinomycin D binds strongly to d(CGACGACG) and d(CGTCGTCG)

ABSTRACT Earlier calorimetric studies had indicated that despite the absence of a GpC sequence, the self-complementary octamer d(CGTCGACG) binds strongly to actinomycin D (ACTD) with high cooperativity and a 2:1 drug/duplex ratio. A subsequent optical spectral study with related oligomers led us to suggest that ACTD may likely stack at the G - C basepairs of the duplex termini. New findings are reported herein to indicate that despite the lack of complete self-complementarity, oligomers of d(CGXCGXCG) [X = A or 11 motif exhibit unusually strong ACTD affinities with binding constants of roughly 2 x 107 M-1 and binding densities of 1 drug molecule per strand. The ACTD binding affinity for …