Structural modification and protein recognition of DNA modified by N-2-fluorenylacetamide, its 7-iodo derivative, and by N-2-fluorenamine.

Several experimental approaches were used to compare the structural modifications introduced by the binding to DNA of N-hydroxy-N-2-fluorenamine and of N-acetoxy-N-2-fluorenylacetamide and its 7-iodo derivative. In the three binding reactions, the major part of the substitution occurred at C-8 of guanine. Formaldehyde unwinding, hydrolysis by endonuclease S(1), linear electric dichroism, circular dichroism, use of antibodies, unwinding of covalently closed circular DNA, and binding of tripeptide were thus successively examined. Most of the techniques showed marked differences between the different modified DNA's. However, some experiments failed to show discrimination between the induced structural alterations. These specific points are discussed. On the basis of all the available experimental evidence and after examination of the Cory-Pauling-Koltun molecular model, we proposed three models of DNA binding at the C-8 of the guanine residue with 1) the 7-iodo derivative (outside binding) 2), N-acetoxy-N-2-fluorenylacetamide (insertion-denaturation) and 3) N-hydroxy-N-2-fluorenamine (insertion without denaturation).