2–Aminofluorene modified DNA duplex exists in two interchangeable conformations

Abstract
One– and two–dimensional NMR shows that the carcinogen 2–aminofluorene exists in two unique, interchangeable conformations when covalently bound to a model human c–H–ras1 proto–oncogene codon 61 oligomer duplex. In one conformation the 2–aminofluorene moiety protrudes out of the major groove leaving the Watson–Crick base pairing of the cytosine and 2–aminofluorene–guanine bases intact, consistent with the ability of replicating enzymes to bypass the lesion and correctly incorporate cytosine. The second form of the modified oligomer duplex may be representative of a pre–mutagenic conformation in that the 2–aminofluorene moiety is stacked within the DNA helix, disrupting base pairing between the 2–aminofluorene–modified guanine and its complementary cytosine.

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