title: Comparative orientation of the fluorene residue in native DNA modified by N-acetoxy-N-2-acetylaminofluorene and two 7-halogeno derivatives.
abstract: Native calf thymus DNA was reacted with N-acetoxy-N-2-acetylaminofluorene (N-AcO-AAF) and its 7-fluoro and 7-iodo derivatives. Different ways of purification of the fluorene modified DNA samples were checked in order ot obtain a nucleic acid free from all noncovalently bound fluorene residues. The decrease in melting temperature in DNA samples modified by N-AcO-AAF(DNA-AAF) was carefully reinvestigated. From these experiments, we conclude that the melting temperature decrease is equal to 1.15 degree C per percent of modified bases, in DNA-AAF samples. Electric dichroism measurements on sonicated DNA samples modified by the different fluorene derivatives show the fluorene ring perpendicular to the helix axis in the case of the N-AcO-AAF and its fluoro derivative, and lying alone the phosphate-sugar backbone in the case of the iodo derivative. The results presented in this paper, along with those obtained earlier, led us to propose an "insertion-denaturation model" for the mode of binding of N-Aco-AAF and its fluoro derivative, and an "outside binding model" for the iodo derivative. Discrepancies with the data obtained by Chang et al.((1974) Biochemistry 13,2142-2148) concerning the melting temperature decrease and the electric dichroism results are observed and discussed.
mesh_terms: D000099:Acetoxyacetylaminofluorene / Q000031:analogs & derivatives; D001665:Binding Sites; D004247:DNA; D005449:Fluorenes / Q000031:analogs & derivatives; D005461:Fluorine; D007455:Iodine; D008956:Models, Chemical; D009691:Nucleic Acid Denaturation; D013696:Temperature
chemical_list: D005449:Fluorenes; D005461:Fluorine; D000099:Acetoxyacetylaminofluorene; D004247:DNA; D007455:Iodine