Formation of Poly[d(A-T)(2)] Specific Z-DNA by a Cationic Porphyrin

Typical CD spectrum of the right-handed poly[d(A-T)(2)] was reversed when trans-bis(N-methylpyrimidium-4-yl)diphenyl porphyrin (trans-BMPyP) was bound, suggesting that the helicity of the polynucleotide was reversed to the left-handed form. The formation of the left-handed Z-form poly[d(A-T)(2)] was confirmed by (31)P NMR, in which a single (31)P peak of B-form poly[d(A-T)(2)] was split into two peaks, which is similar to the conventional B-Z transition of poly[d(G-C)(2)] induced by the high ionic strength. The observed B-Z transition is unique for poly[d(A-T)(2)]. The other polynucleotides, including poly[d(G-C)(2)], poly(dG)·poly(dC) and poly(dA)·poly(dT) remained as the right-handed form in the presence of the same porphyrin. This observation suggests that the porphyrin array that was formed along the poly[d(A-T)(2)] provides a template to which left-handed poly[d(A-T)(2)] is associated with an electrostatic interaction.