The antitumor antibiotic bleomycin (BLM) binds to and degrades the self-complementary octanucleotide d(CGCTAGCG)(2) in a sequence-selective fashion. To model the binding interaction, 1:1 complexes of Zn(II). BLM A(2) and Zn(II). BLM A(5) with the DNA oligonucleotide have been examined using two-dimensional MMR experiments and restrained molecular dynamics calculations. Intercalation is indicated by the broadening and upfield shifting of the BLM aromatic bithiazole protons and DNA base-paired imino protons. However, the data do not support a classical mode of intercalation, as the sequential intrastrand NOE connectivities of d(CGCTAGCG)(2) are not disrupted upon Zn . BLM binding. The orientation of the drug molecule in the helix is based on the finding of eight intermolecular BLM-DNA NOEs in the Zn . BLM A(5)-d(CGCTAGCG)(2) complex. The bithiazole B-ring proton (Bit 5) and spermidine H3 (Sp 3) atoms are positioned within 5 Angstrom of adenosine(5) H2 in the minor groove, while the bithiazole A-ring proton (Bit 5’) shows major groove contacts to protons of cytidine(3) and thymidine(4). Protons of the beta-hydroxyhistidine and methyl valerate to cytidine(7). Using the NMR-derived NOE distance and dihedral bond angle restraints to guide the molecular dynamics calculations, a binding model for the interaction of Zn . BLM with the octanucleotide was derived. To satisfy the major and minor groove BLM-DNA NOE contacts, this model positions the bithiazole ring system in a "cis" orientation (H atoms on same side) with the H atoms directed into the helix. Such an orientation favors partial stacking interactions between the DNA bases and the bithiazole rings and permits interaction of the cationic spermidine tail and metal binding domain with the minor groove of the helix.