Yajima H, Takao M, Yasuhira S, Zhao J H, Ishii C, Inoue H, Yasui A
Institute of Development, Aging and Cancer, Tohoku University, Sendai, Japan.
EMBO J. 1995 May 15;14(10):2393-9. doi: 10.1002/j.1460-2075.1995.tb07234.x.
Many eukaryotic organisms, including humans, remove ultraviolet (UV) damage from their genomes by the nucleotide excision repair pathway, which requires more than 10 separate protein factors. However, no nucleotide excision repair pathway has been found in the filamentous fungus Neurospora crassa. We have isolated a new eukaryotic DNA repair gene from N.crassa by its ability to complement UV-sensitive Escherichia coli cells. The gene is altered in a N.crassa mus-18 mutant and responsible for the exclusive sensitivity to UV of the mutant. Introduction of the wild-type mus-18 gene complements not only the mus-18 DNA repair defect of N.crassa, but also confers UV-resistance on various DNA repair-deficient mutants of Saccharomyces cerevisiae and a human xeroderma pigmentosum cell line. The cDNA encodes a protein of 74 kDa with no sequence similarity to other known repair enzymes. Recombinant mus-18 protein was purified from E.coli and found to be an endonuclease for UV-irradiated DNA. Both cyclobutane pyrimidine dimers and (6-4)photoproducts are cleaved at the sites immediately 5' to the damaged dipyrimidines in a magnesium-dependent, ATP-independent reaction. This mechanism, requiring a single polypeptide designated UV-induced dimer endonuclease for incision, is a substitute for the role of nucleotide excision repair of UV damage in N.crassa.
包括人类在内的许多真核生物通过核苷酸切除修复途径去除其基因组中的紫外线（UV）损伤，该途径需要10多种不同的蛋白质因子。然而，在丝状真菌粗糙脉孢菌中尚未发现核苷酸切除修复途径。我们从粗糙脉孢菌中分离出一个新的真核DNA修复基因，该基因能够互补对紫外线敏感的大肠杆菌细胞。该基因在粗糙脉孢菌mus-18突变体中发生改变，并导致该突变体对紫外线具有独特的敏感性。导入野生型mus-18基因不仅能互补粗糙脉孢菌的mus-18 DNA修复缺陷，还能赋予酿酒酵母的各种DNA修复缺陷突变体和人类着色性干皮病细胞系紫外线抗性。该cDNA编码一种74 kDa的蛋白质，与其他已知的修复酶没有序列相似性。重组mus-18蛋白从大肠杆菌中纯化出来，发现它是一种针对紫外线照射DNA的核酸内切酶。在镁依赖、不依赖ATP的反应中，环丁烷嘧啶二聚体和（6-4）光产物都在受损二嘧啶紧邻的5'位点被切割。这种机制，即需要一种单一的多肽（称为紫外线诱导二聚体核酸内切酶）进行切割，是粗糙脉孢菌中紫外线损伤核苷酸切除修复作用的替代机制。
