GENOMIC DISTRIBUTION AND PHYLOGENY OF DNA REPAIR

我们将确定氧化损伤DNA的碱基切除修复是否 碱基优先出现在活跃转录的基因中。 修复 5-羟甲基尿嘧啶（HmUra），由HmUra-DNA糖基化酶修复 并且不阻断复制，将与胸腺嘧啶乙二醇进行比较 及相关病变的修复。大肠杆菌核酸内切酶III和DO 块复制。 HmUra-DNA糖基化酶是一种独特的修复酶， 没有细菌和酵母。 我们建议， 系统发育分布反映了它的主要功能， DNA中5-甲基胞嘧啶残基。 相反，内切核酸酶III样 活性在遗传学上是保守的，表明病变 所有物种都有这种酶修复的基因。 这些病变包括 UV诱导的嘧啶水合物。 胞嘧啶的水合作用导致 不可逆脱氨形成尿嘧啶水合物，如果不修复， 点突变 5-甲基胞嘧啶也可能发生这种反应 残留物导致不可逆的脱氨基作用形成胸腺嘧啶水合物。 我们将 研究嘧啶光水合物的形成和稳定性， 使用E.杆菌内切核酸酶 三、作为一种探索 我们将使用这些寡核苷酸作为底物， 将哺乳动物内切核酸酶III样活性纯化至纯度 足以获得蛋白质序列和分子克隆。 结果 这些实验将增加我们的知识的形成和修复 氧化和光化学损伤的DNA，并可能阐明 这种损害与光化性和自发性 癌

We will determine whether base excision repair of oxidatively damaged DNA bases occurs preferentially in actively transcribed genes. The repair of 5-hydroxymethyluracil (HmUra), which is repaired by HmUra-DNA glycosylase and does not block replication, will be compared to that of thymine glycol and related lesions which are repaired by E. coli endonuclease III and do block replication. HmUra-DNA glycosylase is unique among repair enzymes in being absent from bacteria and yeast. We have proposed that its phylogenetic distribution reflects its major function which is the repair of 5-methylcytosine residues in DNA. In contrast, endonuclease III-like activities are phylogenetically conserved indicating that the lesions repaired by the enzymes are formed in all species. Among these lesions are UV induced pyrimidine hydrates. The hydration of cytosine leads to irreversible deamination to uracil hydrate which, if unrepaired, leads to point mutations. This reaction scheme may also occur for 5-methylcytosine residues leading to irreversible deamination to thymine hydrate. We will study the formation and stability of pyrimidine photohydrates in oligonucleotides of high specific radioactivity using E. coli endonuclease III as a probe. We will use these oligonucleotides as substrates for the purification of mammalian endonuclease III-like activities to a purity sufficient to obtain protein sequence and molecular cloning. The results of these experiments will add to our knowledge of the formation and repair of oxidative and photochemical damage to DNA and possibly elucidate the relationship of such damage to the etiology of actinic and spontaneous cancer.