Short Communication Base displacement in AAF-modified Z-DNA

A new model is presented for acetylaminofluorene (AAF> modified Z-DNA, in which the carcinogen is in a base-displaced position, inserted into the helix interior and parallel with an adjacent base. The base displacement or the equivalent insertion-denatura-tion model is consistent with a large body of experimental data obtained for random sequence DNA modified with ace-tylaminofluorene (AAF)*. Taken together, the data reveal that the carcinogen is stacked with the adjacent base, and that this results in partial denaturation of the DNA, as well as kinking of the helix axis (1-6). These distortions are imposed on the B form, which predominates in solutions of DNA with random sequence. By contrast, when poly(dG-dQ.poly(dG-dQ is modified with AAF, an inversion in the circular dichroism spectrum i