文摘
The oligodeoxynucleotide 5鈥?CGCATXGAATCC-3鈥猜?鈥?GGATTCAATGCG-3鈥?containing 1,N2-etheno-2鈥?deoxyguanosine (1,N2-蔚dG) opposite deoxyadenosine (named the 1,N2-蔚dG路dA duplex) models the mismatched adenine product associated with error-prone bypass of 1,N2-蔚dG by the Sulfolobus solfataricus P2 DNA polymerase IV (Dpo4) and by Escherichia coli polymerases pol I exo鈥?/i> and pol II exo鈥?/i>. At pH 5.2, the Tm of this duplex was increased by 3 掳C as compared to the duplex in which the 1,N2-蔚dG lesion is opposite dC, and it was increased by 2 掳C compared to the duplex in which guanine is opposite dA (the dG路dA duplex). A strong NOE between the 1,N2-蔚dG imidazole proton and the anomeric proton of the attached deoxyribose, accompanied by strong NOEs to the minor groove A20 H2 proton and the mismatched A19 H2 proton from the complementary strand, establish that 1,N2-蔚dG rotated about the glycosyl bond from the anti to the syn conformation. The etheno moiety was placed into the major groove. This resulted in NOEs between the etheno protons and T5 CH3. A strong NOE between A20 H2 and A19 H2 protons established that A19, opposite to 1,N2-蔚dG, adopted the anti conformation and was directed toward the helix. The downfield shifts of the A19 amino protons suggested protonation of dA. Thus, the protonated 1,N2-蔚dG路dA base pair was stabilized by hydrogen bonds between 1,N2-蔚dG N1 and A19 N1H+ and between 1,N2-蔚dG O9 and A19N6H. The broad imino proton resonances for the 5鈥? and 3鈥?flanking bases suggested that both neighboring base pairs were perturbed. The increased stability of the 1,N2-蔚dG路dA base pair, compared to that of the 1,N2-蔚dG路dC base pair, correlated with the mismatch adenine product observed during the bypass of 1,N2-蔚dG by the Dpo4 polymerase, suggesting that stabilization of this mismatch may be significant with regard to the biological processing of 1,N2-蔚dG.