ALTERED DNA LIGASE I IN CANCER-PRONE HEREDITARY DISEASE

来自Bloom综合征（BS）患者的细胞， 与癌症发生率增加相关的遗传性疾病， 染色体异常 其中包括增加 自发姐妹染色单体交换（SCE）率， 染色体畸变;连同慢复制子叉 DNA链成熟的进展和延迟速率;以及 对DNA损伤剂的敏感性略有增加。 几 这些特征也是E.大肠杆菌和酵母突变体 有缺陷的DNA连接酶 我们最近发现BS中DNA连接酶I活性存在缺陷， 细胞，而DNA连接酶II，DNA聚合酶- α和β没有改变。 无法正确结扎 DNA在复制、修复或重组过程中断裂， 解释了BS的许多疾病，包括 增加患癌症的风险。 本建议的目的是：（1）确定是否减少 酶活性与蛋白质分子的减少相关 在BS细胞中使用免疫印迹、连接酶-AM（32P）加合物测定，以及 SDS-凝胶电泳; 2）为了纯化酶，比较 正常和异常细胞的结构和生化特性 连接酶I，产生抗体，并鉴定改变的结构域; 3） 筛选其他癌症易感细胞、突变体、正常BS细胞杂交体， 和肿瘤前组织中连接酶的异常;最后， 4)克隆正常和异常的连接酶I基因，并校正 通过显微注射连接酶蛋白和/或转染的BS缺陷 连接酶基因。 癌症易感基因的分子本质的阐明 疾病很可能提供新的见解的机制， DNA处理和推导的强制性步骤（S）在 引发人类癌症。

Cells from patients with Bloom's syndrome (BS), an autosomal inherited disorder associated with increased cancer frequency, exhibit chromosomal abnormalities. These include an increased rate of spontaneous sister chromatid exchanges (SCE) and chromosomal aberrations; together with slow replicon fork progression and a retarded rate of DNA chain maturation; and slightly increased sensitivity to DNA damaging agents. Several of these features are also characteristic of E. coli and yeast mutants with a defective DNA ligase. We recently found that DNA ligase I activity was defective in BS cells, whereas the activities of DNA ligase II, DNA polymerase- alpha and -beta were not altered. The inability to properly ligate DNA breaks during replication, repair, or recombination may account for the many disorders of BS, including the greatly increased risk of cancer. The aim of this proposal is: 1) to determine if the decrease in enzyme activity correlates with the decrease in protein molecules in BS cells using immunoblot, ligase-AM(32P) adduct assay, and SDS-gel electrophoresis; 2) to purify the enzymes, compare the structural and biochemical properties of normal and aberrant ligase I, raise antibodies, and to identify the altered domain; 3) to screen other cancer-prone cells, mutants, normal-BS cell hybrids, and pre-neoplastic tissues for abnormalities in ligases; and finally, 4) to clone the normal and aberrant ligase I genes, and correct the BS defect by microinjection of ligase protein and/or transfection of the ligase gene. The elucidation of the molecular nature of cancer-prone genetic diseases may well provide new insights into the mechanism of DNA processing and deduction of the obligatory step(s) in the initiation of human cancer.