Hwang J R, Moncollin V, Vermeulen W, Seroz T, van Vuuren H, Hoeijmakers J H, Egly J M
Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM, 1 rue Laurent Fries, B. P. 163, 67404 Illkirch Cédex, C. U. de Strasbourg, France.
J Biol Chem. 1996 Jul 5;271(27):15898-904. doi: 10.1074/jbc.271.27.15898.
XPB is a subunit of the basal transcription factor TFIIH, which is also involved in nucleotide excision repair (NER) and potentially in cell cycle regulation. A frameshift mutation in the 3'-end of the XPB gene is responsible for a concurrence of two disorders: xeroderma pigmentosum (XP) and Cockayne's syndrome (CS). We have isolated TFIIH from cells derived from a patient (XP11BE) who carries this frameshift mutation (TFIIHmut) and from the mother of this patient (TFIIHwt) to determine the biochemical consequences of the mutation. Although identical in composition and stoichiometry to TFIIHwt, TFIIHmut shows a reduced 3' --> 5' XPB helicase activity. A decrease in helicase and DNA-dependent ATPase activities was also observed with the mutated recombinant XPB protein. The XPB mutation causes a severe NER defect. In addition, we provide evidence for a decrease in basal transcription activity in vitro. The latter defect may provide an explanation for many of the XP and CS symptoms that are difficult to rationalize based solely on an NER defect. Thus, this work presents the first detailed analysis of a naturally occurring mutation in a basal transcription factor and supports the concept that the combined XP/CS clinical entity is actually the result of a combined transcription/repair deficiency.
XPB是基础转录因子TFIIH的一个亚基，它也参与核苷酸切除修复（NER），并可能参与细胞周期调控。XPB基因3'端的一个移码突变导致了两种疾病的并发：着色性干皮病（XP）和科凯恩综合征（CS）。我们从携带这种移码突变的患者（XP11BE）及其母亲（TFIIHwt）的细胞中分离出了TFIIH，以确定该突变的生化后果。尽管TFIIHmut在组成和化学计量上与TFIIHwt相同，但它的3'→5' XPB解旋酶活性降低。在突变的重组XPB蛋白中也观察到解旋酶和依赖DNA的ATP酶活性的降低。XPB突变导致严重的NER缺陷。此外，我们提供了体外基础转录活性降低的证据。后一种缺陷可能为许多仅基于NER缺陷难以解释的XP和CS症状提供了解释。因此，这项工作首次对基础转录因子中的自然发生突变进行了详细分析，并支持了XP/CS联合临床实体实际上是转录/修复联合缺陷结果的概念。
