ISOLATION AND STRUCTURAL CHARACTERIZATION OF A CDNA CLONE ENCODING THE HUMAN DNA-REPAIR PROTEIN FOR O-6-ALKYLGUANINE
ISOLATION AND STRUCTURAL CHARACTERIZATION OF A CDNA CLONE ENCODING THE HUMAN DNA-REPAIR PROTEIN FOR O-6-ALKYLGUANINE
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DOI：
10.1073/pnas.87.2.686
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发表时间：
1990-01-01
影响因子：
11.1
通讯作者：
MITRA, S
中科院分区：
文献类型：
--
作者：
TANO, K;SHIOTA, S;MITRA, S
O 6-甲基鸟嘌呤-DNA甲基转移酶（MGMT; DNA-O 6-methylguanine：protein-L-cysteine S-methyltransferase，EC 2.1.1.63）是存在于大多数生物体中的一种独特的DNA修复蛋白，通过在自杀反应中化学计量地接受半胱氨酸残基上的烷基，从DNA中去除致癌和致突变的加合物O 6-烷基鸟嘌呤。哺乳动物蛋白质在体细胞和生殖系细胞中都受到高度调控。此外，某些烷化剂在肿瘤和正常细胞中的毒性与这种蛋白质的水平呈负相关。人基因的cDNA，此后命名为MGMT，已被克隆在表达载体的基础上，其拯救甲基转移酶缺陷（ada-）大肠杆菌宿主。该cDNA完全编码一个22 kDa的活性甲基转移酶，其氨基酸序列为61个残基，与E.大肠杆菌甲基转移酶（ADA和OGT基因的产物），其包含烷基受体残基。人cDNA与ada和ogt基因没有序列相似性，部分原因是密码子使用的差异，并且与E. coli基因组DNA。然而，它与人、小鼠和大鼠DNA的不同限制性片段杂交。在许多人类细胞系中观察到的甲基转移酶的缺乏是由于MGMT基因的缺乏或其0.95-腺苷酸酶poly（A）+ RNa转录物的合成和/或稳定性的缺乏。
O6-Methylguanine-DNA methyltransferase (MGMT; DNA-O6-methylguanine:protein-L-cysteine S-methyltransferase, EC 2.1.1.63), a unique DNA repair protein present in most organisms, removes the carcinogenic and mutagenic adduct O6-alkylguanine from DNA by stoichiometrically accepting the alkyl group on a cysteine residue in a suicide reaction. The mammalian protein is highly regulated in both somatic and germ-line cells. In addition, the toxicity of certain alkylating drugs in tumor and normal cells is inversely related to the levels of this protein. The cDNA of the human gene, henceforth named MGMT, has been cloned in an expression vector on the basis of its rescue of a methyltransferase-deficient (ada-) Escherichia coli host. A 22-kDa active methyltransferase encoded entirely by the cDNA contains an amino acid sequence of 61 residues that bears 60-65% similarity with segments of E. coli methyltransferase (products of the ada and ogt genes), which encompass the alkyl-acceptor residues. The human cDNA has no sequence similarity with the ada and ogt genes, due in part to differences in codon usage, and shows no detectable homology with E. coli genomic DNA. However, it hybridizes with distinct restriction fragments of human, mouse, and rat DNAs. The lack of methyltransferase observed in many human cell lines is due to the absence of the MGMT gene or to lack of synthesis and/or stability of its 0.95-kilobase poly(A)+ RNa transcript.