The goal is to understand relationships between conformational perturbations of DNA which has been adducted by endogenous and exogenous chemical mutagens, and the subsequent biological processing of adducted DNA, e.g., during error-prone replication. We seek to understand what features of adduct structure promote frameshifts vs. substitutions. Using a frameshift-prone sequence from the Salmonella typhimurium hisD3052 gene, we will examine whether the primary adduct of malondialdehyde, M1G, induces frameshift mutations as a consequence of the ability of duplex DNA to spontaneously ring-open this adduct to its derivative N2-(3-oxo-l-propenyl)-dG. We propose that N2-(3-oxo-l- propenyl)-dG induces/promotes strand slippage structures subsequent to incorporation of dCTP, possibly as a consequence of the positioning of the propenyl moiety in the minor groove of the duplex, fostering dissociation/reassociation of the polymerase due to potential disruption of protein DNA interactions involving the thumb region of the polymerase. We will examine the potential formation of DNA crosslinks by the N2-(3-oxo-l-propenyl)-dG derivative. We will examine why the planar intercalated trans-8,9-dihydro-8-(N7-guanyl)-9-hydroxyaflatoxin B1 adduct is not a strong inducer of frameshifts, using the codon 249 sequence of the p53 tumor suppressor gene, which has been linked to human cancer via aflatoxin-induced G yields T mutations. This adduct stabilizes DNA, and perhaps discourages strand slippage intermediates, which we propose reduces the propensity for frameshifts. The adduct may not disrupt minor groove interactions between DNA polymerase and the duplex. We will compare this adduct with its imidazole ring-opened derivative, the FAPY adduct, which induces greater stabilization of the DNA duplex. We will examine structural hypotheses to explain the G yields T and G yields A transitions induced by the trans-8,9-dihydro-8- (N7-guanyl)-9-hydroxyaflatoxin B1. A proposed mechanism for the """"""""signature"""""""" 5'-neighbor mutation C yields T will be examined. Our working hypothesis posits that the adduct alters or inhibits extension following the correct incorporation of cytosine, possibly by misaligning the primer terminous for further extension.
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