NEW HUMAN DNA REPAIR ENDONUCLEASE

描述：(改编自调查人员的摘要)维护 基因组的完整性依赖于DNA修复系统的有效性。这些 系统中和外源基因对DNA的突变负担 攻击、内源性反应物种和错误 复制。DNA监测和修复机制的失败导致了 突变率的增加，这反过来又会导致易感性 致癌。在避免突变和基因组稳定性方面的突出作用 是由DNA错配修复系统执行的。这个系统处理基地 配对错配、短插入/短缺失和重组衍生 异源双链。遗传性非息肉病性结直肠癌患者 (HNPCC)在参与DNA错配修复的基因中携带胚系突变 (h MSH2、h MLH1、GTBP/hMSH6、hPMS2和hPMS1)。这些基因编码人类 大肠杆菌错配修复蛋白MutS和MutL的同源物。在 细菌系统，第三种蛋白质，单链内切酶Muth， 执行识别链的关键功能，切割新的 合成了携带突变的DNA链。新的链被识别出来 由于GATC位点暂时缺乏腺嘌呤甲基化。至 Date，Muth的真核同源物，即真核错配修复 内切酶，还没有被鉴定，分子决定因素 缺乏GATC甲基化的真核细胞的链识别 仍然难以捉摸。通过利用酵母与hMLH1的相互作用陷阱 作为诱饵，人类编码新基因MED1(错配修复内切酶1) 克隆了一个与细菌核酸内切酶同源的蛋白质。数列 对MED1的分析提示了一种可能的链识别机制 CpG位点上的胞嘧啶甲基化。与hMLH1和 与细菌DNA修复蛋白同源，MED1是一个假定的错配 修复蛋白，可能是长期寻找的真核功能同源物 穆斯。由于错配修复基因在HNPCC和散发性癌症中发生突变 MED1微卫星不稳定性是肿瘤遗传的候选基因 测试。基于这些观察，建议进行实验以解决以下问题： 1)MED1的生化性质；2)其在DNA修复中的作用。 这些研究可能为真核生物的机制提供新的见解。 错配修复和进一步的DNA缺陷修复和 癌症。

DESCRIPTION: (adapted from the investigator's abstract) The maintenance of genomic integrity relies on the efficacy of DNA repair systems. These systems counteract the mutational burden imposed on DNA by exogenous attacks, endogenous reactive species, and errors originating during replication. Failure of DNA surveillance and repair mechanisms leads to an increase in the mutation rate, and this, in turn, results in predisposition to cancer. A prominent role in mutational avoidance and genomic stability is performed by the DNA mismatch repair system. This system handles base pair mismatches, short insertions/deletions and recombination-derived heteroduplexes. Patients with Hereditary Non-Polyposis Colorectal Cancer (HNPCC) carry a germline mutation in genes involved in DNA mismatch repair (h MSH2, h MLH1, GTBP /hMSH6, hPMS2 and hPMS1). These genes encode human homologues of the E. coli mismatch repair proteins MutS and MutL. In the bacterial system, a third protein, the single-strand endonuclease MutH, performs the crucial function of strand recognition, incising the newly synthesized DNA strand carrying the mutation. The new strand is identified by virtue of the transient lack of adenine methylation at GATC sites. To date, eukaryotic homologues of MutH, i.e. eukaryotic mismatch repair endonucleases, have not been identified, and the molecular determinants of strand discrimination in eukaryotic cells - which lack GATC methylation - have remained elusive. By employing the yeast interaction trap with hMLH1 as bait , MED1 (mismatch repair endonuclease1), a novel human gene encoding a protein with homology to bacterial endonucleases, was cloned. Sequence analysis of MED1 suggests a possible mechanism of strand recognition based on cytosine methylation at CpG sites. For its interaction with hMLH1 and homology to bacterial DNA repair proteins, MED1 is a putative mismatch repair protein and might be a long sought eukaryotic functional homologue of MutH. Since mismatch repair genes are mutated in HNPCC and sporadic cancers with microsatellite instability, MED1 is a candidate gene for cancer genetic testing. Based in these observations, experiments are proposed to address: 1) the biochemical properties of MED1; 2) its functional role in DNA repair. These studies may provide new insights into the mechanisms of eukaryotic mismatch repair and further the link between defective DNA repair and cancer.