Venkatarangan L, Sivaprasad A, Johnson F, Basu A K
Department of Chemistry, University of Connecticut, Storrs, CT 06269-3060, USA.
Nucleic Acids Res. 2001 Apr 1;29(7):1458-63. doi: 10.1093/nar/29.7.1458.
2-Nitropropane (2-NP), an important industrial solvent and a component of cigarette smoke, is mutagenic in bacteria and carcinogenic in rats. 8-Amino-2'-deoxyguanosine (8-amino-dG) is one of the types of DNA damage found in liver, the target organ in 2-NP-treated rats. To investigate the thermodynamic properties of 8-amino-dG opposite each of the four DNA bases, we have synthesized an 11mer, d(CCATCGCTACC), in which G represents the modified base. By annealing a complementary DNA strand to this modified 11mer, four sets of duplexes were generated each containing one of the four DNA bases opposite the lesion. Circular dichroism studies indicated that 8-amino-dG did not alter the global helical properties of natural right-handed B-DNA. The thermal stability of each duplex was examined by UV melting measurements and compared with its unmodified counterpart. For the unmodified 11mer, the relative stability of the complementary DNA bases opposite G was in the order C > T > G > A, as determined from their -DeltaG degrees values. The free energy change of each modified duplex was lower than its unmodified counterpart, except for the G*:G pair that exhibited a higher melting transition and a larger -DeltaG degrees than the G:G duplex. Nevertheless, the stability of the modified 11mer duplex also followed the order C > T > G > A when placed opposite 8-amino-dG. To explore if 8-amino-dG opposite another 8-amino-dG has any advantage in base pairing, a G*:G* duplex was evaluated, which showed that the stability of this duplex was similar to the G*:G duplex. Mutagenesis of 8-amino-dG in this sequence context was studied in Escherichia coli, which showed that the lesion is weakly mutagenic (mutation frequency approximately 10(-3)) but still can induce a variety of targeted and semi-targeted mutations.
2-硝基丙烷（2-NP）是一种重要的工业溶剂，也是香烟烟雾的成分之一，它在细菌中具有致突变性，在大鼠中具有致癌性。8-氨基-2'-脱氧鸟苷（8-氨基-dG）是在2-NP处理的大鼠的靶器官肝脏中发现的DNA损伤类型之一。为了研究8-氨基-dG与四种DNA碱基相对时的热力学性质，我们合成了一个11聚体d(CCATCGCTACC)，其中G代表修饰碱基。通过将互补DNA链与这个修饰的11聚体退火，产生了四组双链体，每组双链体都包含与损伤相对的四种DNA碱基之一。圆二色性研究表明，8-氨基-dG不会改变天然右手B-DNA的整体螺旋性质。通过紫外熔解测量检查了每个双链体的热稳定性，并与其未修饰的对应物进行了比较。对于未修饰的11聚体，根据其-ΔG°值确定，与G相对的互补DNA碱基的相对稳定性顺序为C>T>G>A。除了G*:G对表现出比G:G双链体更高的熔解转变和更大的-ΔG°外，每个修饰双链体的自由能变化都低于其未修饰的对应物。然而，当与8-氨基-dG相对时，修饰的11聚体双链体的稳定性也遵循C>T>G>A的顺序。为了探索8-氨基-dG与另一个8-氨基-dG相对时在碱基配对方面是否有任何优势，评估了一个G*:G双链体，结果表明该双链体的稳定性与G:G双链体相似。在大肠杆菌中研究了该序列背景下8-氨基-dG的诱变作用，结果表明该损伤具有弱诱变作用（突变频率约为10^(-3)），但仍可诱导多种靶向和半靶向突变。
