Vidal A, Abril N, Pueyo C
Departamento de Bioquimica y Biologia Molecular, Universidad de Cordoba, Espana.
Environ Mol Mutagen. 1997;29(2):180-8. doi: 10.1002/(sici)1098-2280(1997)29:2<180::aid-em9>3.0.co;2-i.
To determine the influence of DNA repair by Ogt alkyltransferase on the distribution of alkylnitrosourea-induced mutations, we have analysed in Ogt-proficient and Ogt-deficient bacterial strains the DNA sequence changes of a total of 357 independent mutations occurring within the initial part of the lacl gene of Escherichia coli. The majority (>80%) of mutations induced by either N-ethyl-N nitrosourea (ENU) or N-methyl-N-nitrosourea (MNU) in the two genetic backgrounds were G:C --> A:T transitions, consistent with the predominant role of the O6-alkylguanine miscoding lesion in mutagenesis by alkylating agents. The analysis of the distribution of G:C --> A:T transitions induced by ENU in Ogt+ and Ogt bacteria reveals an influence of the 5'-flanking base at the level of repair by Ogt alkyltransferase. The Ogt protein appears more efficient at repairing O6-ethylguanine lesions, which are flanked 5' by a G or C, in agreement with previously reported data from our group for ethylmethane sulfonate. In contrast, no preference could be inferred for the repair of O6-methylguanine lesions by Ogt protein. These results seem to indicate that the preference of the Ogt alkyltransferase to repair certain DNA sequences might be a function of the size of the alkyl group. The importance of the alkyl group length has been described also at the level of the (A)BC excinuclease machinery that seems to have a DNA sequence specificity opposite to that of Ogt alkyltransferose.
为了确定Ogt烷基转移酶介导的DNA修复对烷基亚硝基脲诱导突变分布的影响，我们分析了在Ogt功能正常和Ogt缺陷的细菌菌株中，大肠杆菌lacl基因起始部分总共357个独立突变的DNA序列变化。在这两种遗传背景下，由N-乙基-N-亚硝基脲（ENU）或N-甲基-N-亚硝基脲（MNU）诱导的大多数突变（>80%）是G:C→A:T转换，这与O6-烷基鸟嘌呤错配损伤在烷基化剂诱变中的主要作用一致。对ENU在Ogt+和Ogt细菌中诱导的G:C→A:T转换分布的分析揭示了Ogt烷基转移酶在修复水平上5'-侧翼碱基的影响。Ogt蛋白在修复5'侧翼为G或C的O6-乙基鸟嘌呤损伤时似乎更有效，这与我们小组先前报道的关于甲磺酸乙酯的数据一致。相比之下，无法推断Ogt蛋白对O6-甲基鸟嘌呤损伤修复的偏好。这些结果似乎表明，Ogt烷基转移酶对某些DNA序列修复的偏好可能是烷基大小的函数。烷基长度的重要性在（A）BC核酸外切酶机制水平上也有描述，该机制似乎具有与Ogt烷基转移酶相反的DNA序列特异性。
