Ramseier T M, Winteler H V, Hennecke H
Mikrobiologisches Institut, Eidgenössische Technische Hochschule, ETH-Zentrum, Zürich, Switzerland.
J Biol Chem. 1991 Apr 25;266(12):7793-803.
We report the DNA sequence and mutational analysis of a novel cluster of six Bradyrhizobium japonicum genes of which at least three (designated cycV, cycW, and cycX) are essential for the formation of all cellular c-type cytochromes. Mutants having insertions in these genes were completely devoid of any soluble (periplasmic) or membrane-bound c-type cytochromes; even the apo form of cytochrome c1 was not detectable, neither in the membrane nor in the soluble fraction. As a consequence, the mutants had pleiotropic phenotypes such as defects in nitrate respiration, H2 oxidation, electron transport to cytochrome alpha alpha 3, and microaerobic respiration during symbiosis. A fourth open reading frame (ORF132) encoded a protein that might also be concerned with cytochrome c formation, but perhaps only indirectly. The other two open reading frames did not appear to function in this process. The predicted amino acid sequences of the cycW and cycX gene products suggested that these proteins were membrane-bound. The cycV gene product showed extensive similarity to the ATP-binding subunit of a superfamily of membrane-associated transport systems. The predicted ORF132 product was strikingly similar to bacterial thioredoxins and eukaryotic protein disulfide isomerase. Based on these findings it is possible that these proteins are members of a complex transport system involved in the biogenesis of all cytochromes c.
我们报道了日本慢生根瘤菌中一个由六个基因组成的新基因簇的DNA序列及突变分析，其中至少三个基因（命名为cycV、cycW和cycX）对于所有细胞c型细胞色素的形成至关重要。在这些基因中插入突变的突变体完全缺乏任何可溶性（周质）或膜结合的c型细胞色素；甚至细胞色素c1的脱辅基形式在膜中或可溶性部分都检测不到。因此，这些突变体具有多效性表型，如硝酸盐呼吸、H2氧化、向细胞色素αα3的电子传递以及共生期间的微需氧呼吸缺陷。第四个开放阅读框（ORF132）编码一种可能也与细胞色素c形成有关的蛋白质，但可能只是间接相关。另外两个开放阅读框在此过程中似乎不起作用。cycW和cycX基因产物的预测氨基酸序列表明这些蛋白质是膜结合的。cycV基因产物与膜相关运输系统超家族的ATP结合亚基具有广泛的相似性。预测的ORF132产物与细菌硫氧还蛋白和真核蛋白质二硫键异构酶惊人地相似。基于这些发现，这些蛋白质有可能是参与所有细胞色素c生物合成的复杂运输系统的成员。
