Ludlum D B, Mehta J R, Tong W P
Cancer Res. 1986 Jul;46(7):3353-7.
Previous studies have shown that the haloethylnitrosoureas introduce the cross-link 1-(3-deoxycytidyl),2-(1-deoxyguanosinyl)ethane into DNA. This structure is evidently formed by the following sequence of events: an initial attack of a haloethyl group on the O6 position of guanine, formation of the reactive intermediate, 1,O6-ethanoguanine, and reaction of this intermediate with deoxycytidine in the opposite DNA strand. To investigate the role of O6-alkylguanine-DNA alkyltransferase in preventing the formation of this cross-link, a DNA substrate containing O6-fluoroethylguanine has been prepared by reacting DNA with N-2-fluoroethyl-N'-cyclohexyl-N-nitrosourea. The O6-fluoroethylguanine content of this substrate decreases when it is incubated at 37 degrees C and pH 7.8 in the absence of repair factors because of the chemical instability of O6-fluoroethylguanine; however, this loss is accelerated by the addition of rat liver O6-alkylguanine-DNA alkyltransferase, indicating that this repair factor recognizes and repairs O6-fluoroethylguanine in DNA; furthermore, by using [chloroethyl-14C]N-chloroethyl-N'-cyclohexyl-N-nitrosourea, it can be shown directly that the addition of rat liver O6-alkylguanine-DNA alkyltransferase prevents 1-(3-deoxycytidyl),2-(1-deoxyguanosinyl)ethane formation. These studies link the presence of repair activity to the prevention of a specific cytotoxic lesion in DNA.
先前的研究表明，卤代乙基亚硝基脲会将交联物1-(3-脱氧胞苷基)，2-(1-脱氧鸟苷基)乙烷引入DNA中。这种结构显然是由以下一系列事件形成的：卤代乙基首先攻击鸟嘌呤的O6位，形成反应中间体1，O6-乙基鸟嘌呤，然后该中间体与互补DNA链中的脱氧胞苷反应。为了研究O6-烷基鸟嘌呤-DNA烷基转移酶在防止这种交联形成中的作用，通过使DNA与N-2-氟乙基-N'-环己基-N-亚硝基脲反应，制备了含有O6-氟乙基鸟嘌呤的DNA底物。由于O6-氟乙基鸟嘌呤的化学不稳定性，当该底物在37℃和pH值7.8下孵育且不存在修复因子时，其O6-氟乙基鸟嘌呤含量会降低；然而，添加大鼠肝脏O6-烷基鸟嘌呤-DNA烷基转移酶会加速这种损失，这表明该修复因子能够识别并修复DNA中的O6-氟乙基鸟嘌呤；此外，通过使用[氯乙基-14C]N-氯乙基-N'-环己基-N-亚硝基脲，可以直接表明添加大鼠肝脏O6-烷基鸟嘌呤-DNA烷基转移酶可防止1-(3-脱氧胞苷基)，2-(1-脱氧鸟苷基)乙烷的形成。这些研究将修复活性的存在与预防DNA中特定的细胞毒性损伤联系起来。
