The selective B-A conformational transition of the central dinucleotide (CpG) segment of d(CAATCCGGATTG)2 induced by delta-Co(en)3(3+).

The binding of Co(NH3)6(3+), delta-Co(en)3(3+) and delta-Rh(en)3(3+) to the dodecanucleotide d(CAATCCGGATTG)2 has been studied by 1H NMR. Addition of Co(NH3)6(3+), delta-Co(en)3(3+) or delta-Rh(en)3(3+) to d(CAATCCGGATTG)2 induce a similar pattern of chemical shift movements of the dodecanucleotide base protons. Analysis of the chemical shift changes as a function of added metal-ion complex shows that the binding affinity for d(CAATCCGGATTG)2 decreases in the order: delta-Co(en)3(3+) > delta-Rh(en)3(3+) > Co(NH3)6(3+). Addition of a saturating ratio of delta-Co(en)3(3+) to d(CAATCCGGATTG)2 induces a selective B to A type-DNA transition for the central CpG segment of the dodecanucleotide, with all other nucleotide residues maintaining the B-type conformation.