Transcription-coupled repair and its deficiency

核苷酸切除修复（NER）从基因组中去除多种病变，在遗传性疾病着色性干皮病（XP）和科凯恩综合征（CS）中存在缺陷。互补研究发现XP有7个基因参与（XPA-XPG）， CS有2个基因参与（CSA， CSB）。NER有两个亚通路：转录偶联（TC-）NER，它能有效去除阻断转录的病变，以及较慢的全局基因组（GG-）NER。(1)在酵母双杂交系统中，利用XPA结合蛋白2 （XPA-binding protein 2）与XPA相互作用的能力，发现了一个含有855个氨基酸的新蛋白XAB2 (XPA-binding protein 2)，内含18个四肽重复序列。免疫沉淀分析表明XAB2在体内与tc - ner特异性蛋白CSA、CSB和RNA聚合酶II相关。当微注射到活成纤维细胞中时，抗XAB2抗体抑制TCR和转录。这些结果表明XAB2是一个参与TC-NER和转录的新成分。(2) XPA- o - o - o - o -诱导的csb偏向性小鼠较多。当正常发育的xpa缺陷小鼠与csb缺陷小鼠杂交产生双敲除小鼠时，有了一个非常重要的发现。双基因敲除小鼠似乎表现出非常严重的协同发育障碍，导致出生后4-6周极早停止发育和死亡。这些结果表明，CSB和XPA属于不同的上位性类群，DNA损伤和转录能力参与了衰老过程。(3)为了找出NER是否有助于从活性基因中优先去除06-EtGua（如在大鼠乳腺细胞和小鼠胸腺细胞中观察到的），我们在暴露于etnu的XPA +/-和XPA -/-小鼠的不同组织DNA中测量了该管道的修复动力学。对于06-EtGua的组织特异性全局修复，在XPA敲除小鼠和杂合子小鼠之间没有观察到显著差异。然而，在XPA +/-动物的肝脏和脑细胞中，从活性基因中去除这种病变的速度比从总基因组DNA中去除快3-4倍。在XPA敲除小鼠中没有观察到这种优先修复。这些结果表明，活性基因中的06-EtGua被NER修复。少

Nucleotide excision repair (NER) removes a wide variety of lesions from the genome and is defective in the genetic disorders xeroderma pigmentosum (XP) and Cockayne syndrome (CS). Complementation studies revealed that 7 genes are involved in XP (XPA-XPG) and 2 in CS (CSA, CSB). There are two subpathways in NER : transcription-coupled (TC-)NER accomplishing efficient removal of lesions blocking transcription and the slower global genome (GG-)NER.(1) We recently discovered a novel 855-amino acid protein, XAB2 (XPA-binding protein 2), containing 18 tetratricopeptide repeats, by virtue of its ability to interact with XPA in yeast two hybrid system. Immunoprecipitation analysis demonstrated that XAB2 is associated with the TC-NER-specific proteins CSA, CSB and RNA polymerase II in vivo. Antibodies against XAB2 inhibited both TCR and transcription when microinjected into living fibroblasts. These results indicate that XAB2 is a novel component involved in TC-NER and transcription. (2) XPA- o … More r CSB-deflcient mice were generated. A very important discovery was made when XPA-deficient micethat develop normally was crossed with the CSB-deflcient mice to generate double knockout mice. The double knockout mice appear to exhibit very severe synergistic developmental impairment resulting in extremely early ceasing of developmenta and death 4-6 weeks after birth. These results indicate that CSB and XPA belong to the different epistatic groups and that DNA damage and transcriptional competance contribute to the process of aging. (3) To find out whether NER contributes to preferential removal of 06-EtGua from active genes (asobserved in mammary cells of the rat and thymus cells of the mouse) repair kinetics for this a dduct have been measured in DNA from different tissues of EtNU-exposed XPA +/- and XPA -/- mice. For tissue-specific global repair of 06-EtGua no significant differences were observed between XPA knock out and heterozygote mice. However, this lesion was removed 3-4 times faster from active genes than from total genomic DNA in liver and brain cells of XPA +/- animals. This preferential repair was not observed in the XPA knock out mice. These results indicate that 06-EtGua in the active gene is repaired by NER. Less