Concerning the Stereochemistry of Actinomycin Binding to DNA: An Actinomycin-Deoxyguanosine Crystalline Complex

Actinomycin C1(D) is a cyclic polypeptide-containing antibiotic (Fig. 1) which binds to double helical DNA and specifically inhibits RNA synthesis (Kirk, 1960; Kersten et al., 1960; Reich et al., 1961; Goldberg et al., 1962; Hurwitz et al., 1962; for a review, see Reich and Goldberg, 1964). Deoxyguanosine residues are essential for the binding reaction as shown by extensive studies with naturally occurring and synthetic DNA duplexes (Goldberg et al., 1962; Wells and Larson, 1970). The spectral perturbations which accompany actinomycin binding to DNA can be mimicked by the addition of deoxyguanosine to solutions of actinomycin (Kersten, 1961), although similar spectral changes can be induced with a variety of