MUTAGENIC CONSEQUENCES OF DEFINED LESIONS IN DNA

将定义的损伤引入DNA的突变后果是 在能够检测到广谱的突变系统中进行检查 突变事件，无论是在实际地点还是离实际地点一段距离 造成的损害。该系统已首次应用于除杂，损失 脱氧核糖核酸中的嘌呤碱基。这是一种常见的自发损害，也是一种 修复许多其他类型的DNA损伤的常见中间体。 排尿具有很强的致突变性，这是通过将排出的 将MI3mp2 DNA导入SOS诱导的感受态大肠杆菌细胞。DNA序列分析 211个突变表明，大多数突变是碱基替换 反映与非编码碱基位置相反的潮湿的插入 导致了典型的变形。这样的转换是 在活体中经常观察到的几种会产生大块的破坏性物质 DNA加合物，这表明这种加合物可能会产生突变 通过基本部位中间体，或通过简单地排除模板碱基 氢键。 第二个明确的损伤是DNA中的尿嘧啶残留物，原因是 热诱导胞嘧啶脱氨基。建议这是第二个 DNA中最常见的自发性损害，代表着显著的 挑战37摄氏度的细胞。在这些研究中，第一个在体外 本研究建立了一种反转一个脯氨酸密码子的方法。化验结果 既具有高度的特异性，又非常敏感。使用这个和 正向突变实验，C脱氨基的速率常数为 在生理pH和盐浓度及摄氏3 37度时测定。 C脱氨基的序列特异性刚刚开始检测。 最终，各种加合物对跨链质子化的贡献 在双链DNA中，导致C脱氨基，将被调查。

The mutagenic consequences of introducing defined lesions into DNA are being examined in a mutational system capable of detecting a wide spectrum of mutational events, both at and some distance away from the actual site of damage. The system has first been applied to depurination, the loss of a purine base from DNA. This is a frequent spontaneous lesion as well as a common intermediate in the repair of many other types of DNA damage. Depurination is highly mutagenic, as determined by transfecting depurinated MI3mp2 DNA into SOS-induced competent E. coli cells. DNA sequence analysis of 211 mutants demonstrates that most mutations are base substitutions reflecting insertion of dAMP opposite the non-coding abasic site and resulting in characteristic transversions. Such transversions are frequently observed in vivo for several damaging agents which produce bulky DNA adducts, suggesting that such adducts may produce mutations either through an abasic site intermediate, or by simply precluding template base hydrogen bonding. The second defined lesion is a uracil residue in DNA, resulting from the heat-induced deamination of cytosine. This is suggested to be the second most frequent spontaneous lesion in DNA, representing a significant challenge to a cell at 37 degrees C. For these studies, the first in vitro assay for reversion of a proline codon (CCC) has been developed. The assay is both highly specific and very sensitive. Using this and the forward-mutation assay, the rate constant of C deamination has been determined at physiological pH and salt concentrations and 3 37 degrees C. The sequence specificity of C deamination has just come under examination. Eventually, the contribution of cross-strand protonation by various adducts in double-stranded DNA, leading to C deamination, will be investigated.