Sweet J M, Carda B, Small G D
Mutat Res. 1981 Nov;84(1):73-82. doi: 10.1016/0027-5107(81)90050-6.
The removal of 3-methyladenine and 7-methylguanine from nuclear DNA was determined following exposure of Chlamydomonas reinhardi to methyl methanesulfonate (MMS). The amount of 3-methyladenine in DNA was determined using an extract from Micrococcus luteus that has a 3-methyladenine-DNA glycosylase. The amount of 7-methylguanine was estimated by heating the DNA for 30 min at 70 degrees followed by alkaline hydrolysis of the resulting apurinic sites. The molecular weight of the DNA was determined using alkaline sucrose gradients. The 3-methyladenine is removed with a half-life of 2--3 h whereas the 7-methylguanine is removed with a half-life of 10--12 h. The rate of removal of the 7-methylguanine is more than an order of magnitude faster than the estimated non-enzymatic hydrolysis rate indicating the probability of enzymatic repair. Addition of cycloheximide immediately after MMS treatment inhibits the removal of 3-methyladenine and 7-methylguanine from DNA. If cycloheximide is added 1.5 h after treatment with MMS, there is much less inhibition of the removal of 3-methyladenine. These results are interpreted to mean that MMS induces the synthesis of 1 or more proteins that are required for the repair of 3-methyladenine from Chlamydomonas DNA.
莱茵衣藻暴露于甲磺酸甲酯（MMS）后，测定了其核DNA中3 - 甲基腺嘌呤和7 - 甲基鸟嘌呤的去除情况。利用含有3 - 甲基腺嘌呤 - DNA糖基化酶的藤黄微球菌提取物测定DNA中3 - 甲基腺嘌呤的含量。通过将DNA在70℃加热30分钟，然后对产生的脱嘌呤位点进行碱性水解来估算7 - 甲基鸟嘌呤的含量。使用碱性蔗糖梯度测定DNA的分子量。3 - 甲基腺嘌呤的去除半衰期为2 - 3小时，而7 - 甲基鸟嘌呤的去除半衰期为10 - 12小时。7 - 甲基鸟嘌呤的去除速率比估计的非酶促水解速率快一个数量级以上，这表明存在酶促修复的可能性。MMS处理后立即添加环己酰亚胺会抑制DNA中3 - 甲基腺嘌呤和7 - 甲基鸟嘌呤的去除。如果在MMS处理1.5小时后添加环己酰亚胺，对3 - 甲基腺嘌呤去除的抑制作用会小得多。这些结果被解释为意味着MMS诱导了1种或更多种从莱茵衣藻DNA修复3 - 甲基腺嘌呤所需蛋白质的合成。
