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首页> 外文期刊>Journal of Molecular Biology >GENETIC ANALYSIS OF THE FOLDED STRUCTURE OF YEAST MITOCHONDRIAL CYTOCHROME B BY SELECTION OF INTRAGENIC SECOND-SITE REVERTANTS
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GENETIC ANALYSIS OF THE FOLDED STRUCTURE OF YEAST MITOCHONDRIAL CYTOCHROME B BY SELECTION OF INTRAGENIC SECOND-SITE REVERTANTS

机译：通过内源性第二重金属的选择对酵母线粒体细胞色素B的折叠结构进行遗传分析

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The mutations C133 --> Y133, L282 --> F282 and G340 --> E340 in yeast mitochondrial cytochrome b each lead to a dysfunction of the cytochrome bc(1) complex and, consequently, to the absence of growth on non-fermentable substrates. We isolated and characterized, from these mutants, fourteen different intragenic pseudo-revertants of various respiratory sufficient phenotypes. Both first-site and second-site suppressor mutations were found. A novel type of suppressor mutation consisted of the three-base-pair deletion of the parental mutated codon (E340(Delta)). The results provide, for the first time, evidence for the transmembrane disposition of helices F and G of the current eight-helix cytochrome b model. These two helices are presumably in contact with helix C in the folded protein. A simple modelisation study suggests that the packing of helices C, F and G in cytochrome b may be similar to that of helices I, II and VII in bacteriorhodopsin, respectively. We observed from the study of second-site revertants that compensation across the membrane never occurs. For each revertant, the suppressor mutation and the corresponding target mutation are on the same side of the membrane. This membrane sidedness strengthens the topological constraints imposed by the Q-cycle, namely the necessity of spatial separation of two catalytic reaction sites for ubiquinone. [References: 41]
机译：酵母线粒体细胞色素b中的突变C133-> Y133，L282-> F282和G340-> E340均导致细胞色素bc（1）复合物功能障碍，因此导致不可发酵的无生长基材。我们从这些突变体中分离并表征了14种不同的足够呼吸表型的基因内假回复株。发现第一位和第二位抑制子突变。一种新型的抑制突变由亲本突变密码子的三碱基对缺失（E340Δ）组成。该结果首次为当前八螺旋细胞色素b模型的螺旋F和G的跨膜配置提供了证据。这两个螺旋可能与折叠蛋白中的螺旋C接触。一个简单的模型研究表明，细胞色素b中螺旋C，F和G的堆积可能分别与细菌视紫红质中螺旋I，II和VII的堆积相似。从对第二位回复基的研究中我们观察到，从未发生过跨膜的补偿。对于每个回复子，抑制子突变和相应的靶标突变都在膜的同一侧。这种膜的侧面性增强了由Q循环施加的拓扑约束，即必须对泛醌的两个催化反应位点进行空间分离。 [参考：41]

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