Rizvi R Y, Hadi S M
Biosci Rep. 1984 Sep;4(9):729-35. doi: 10.1007/BF01128813.
We have earlier reported that alkylation of DNA by the chemical carcinogen dimethyl sulphate, which mainly alkylates N-7 of guanine and N-3 of adenine, causes the formation of partially denatured regions in double-stranded DNA (Rizvi RY, Alvi NK & Hadi SM, Biosci. Rep. 2, 315-322, 1982). It is known that the major site of alkylation in DNA by N-ethyl-N-nitrosourea (EtNu) are the phosphate groups. N-methyl-N-nitrosourea (MeNu), on the other hand, causes the alkylation of mainly guanine residues. We have therefore studied the effect of these two alkylating carcinogens on the secondary structure of DNA. DNA alkylated with increasing concentrations of EtNu and MeNu was subjected to alkaline and S1 nuclease hydrolysis. Thermal melting profiles of alkylated DNA were also determined using S1 nuclease. The results indicated that alkylation by the two alkylating agents had a differential effect on the secondary structure of DNA. EtNu-alkylated DNA was found to be more thermostable than native DNA at neutral pH. It was however more alkali-labile than MeNu-alkylated DNA. The greater stability of EtNu-alkylated DNA was considered to be due to abolition of negative charges on phosphate alkylation.
我们之前报道过，化学致癌物硫酸二甲酯对DNA的烷基化作用主要使鸟嘌呤的N-7位和腺嘌呤的N-3位烷基化，会导致双链DNA中形成部分变性区域（Rizvi RY、Alvi NK和Hadi SM，《生物科学报告》2，315 - 322，1982年）。已知N-乙基-N-亚硝基脲（EtNu）对DNA的主要烷基化位点是磷酸基团。另一方面，N-甲基-N-亚硝基脲（MeNu）主要使鸟嘌呤残基发生烷基化。因此，我们研究了这两种烷基化致癌物对DNA二级结构的影响。用浓度不断增加的EtNu和MeNu烷基化的DNA进行了碱性水解和S1核酸酶水解。还用S1核酸酶测定了烷基化DNA的热解链曲线。结果表明，这两种烷基化剂的烷基化作用对DNA二级结构有不同影响。发现在中性pH条件下，EtNu烷基化的DNA比天然DNA更耐热。然而，它比MeNu烷基化的DNA对碱更不稳定。EtNu烷基化DNA具有更高稳定性被认为是由于磷酸烷基化消除了负电荷。
