This research project attempts to address fundamental structure-activity relationships that define the role of exocyclic nucleic acid adducts and cross-links in chemical mutagenesis and carcinogenesis. The proposed structural and dynamics measurements on exocyclic adduct lesions and cross-links prepared in Francis Johnson's laboratory (State University of New York, Stony Brook) at specific positions on DNA oligomers of defined sequence will be undertaken in parallel with site-directed mutagenesis studies in the laboratories of the collaborators Arthur Grollman (State University of New York, Stony Brook) and John Essigmann (MIT) to correlate molecular structure with biological function in these systems. Structural features at and adjacent to exocyclic lesions in DNA will be elucidated following analysis of two dimensional NMR parameters using structure-reconstruction procedures while transient base pair opening will be monitored by imino proton hydrogen exchange measurements at the individual base pair level. The NMR studies will address the role of exocyclic ring size and substituent distribution, the contribution of opposing base and flanking base pairs, and the effect of solution pH on the nature of the base pairing, structure and dynamics centered about the lesion suite. The exocyclic adduct will be studied in right-handed and left-handed DNA duplexes, DNA-RNA hybrid helices, bulge sites and carcinogenic hot spot sequences in DNA. The research will be extended to exocyclic adducts positioned across a basic sites and separated by a few base pairs from O-alkyl base adducts to monitor the potential synergism between lesion sites. There are also plans to characterize the proposed 1-(N3-deoxycytidyl)-2-(N1-deoxyguanosinyl) ethane dC-dG cross-linked adduct, as well as alkyl chain cross-links between amino protons of adjacent base pairs located on partner strands. These studies will determine the extent of structural perturbation at the bridged site and its propagation along the helix.
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