Interactions of Mn²⁺ with a non-self-complementary Z-type DNA duplex

Crystal structures of the hexanucleotide d(CACGCG)·d(CGCGTG) were determined in two crystal lattices when different concentrations of the counterion Mn²⁺ were used in crystallization. The availability of Mn²⁺ during the crystallization process appears to play an important role in inducing different crystal packings that lead to crystals belonging to the two space groups P2₁ and P6₅. Analysis of the molecular interactions of Mn²⁺ with the Z-form duplexes shows direct coordination to the purine residues G and A.