Du L, Tibelius K H, Souza E M, Garg R P, Yates M G
Department of Microbiology, McGill University, Quebec, Canada.
J Mol Biol. 1994 Nov 4;243(4):549-57. doi: 10.1016/0022-2836(94)90029-9.
Hydrogen-uptake (Hup) activity in Azotobacter chroococcum depends upon a cluster of genes spread over 13,687 bp of the chromosome. Six accessory genes of the cluster, hupABYCDE, begin 4.8 kb downstream of the structural genes, hupSL, and are required for the formation of a functional [NiFe] hydrogenase. The sequencing of the intervening 4.8 kb of hup-specific DNA has now been completed. This revealed eight additional closely linked ORFs, which we designated hupZ, hupM, hupN, hupO, hupQ, hupR, hupT and hupV. These genes potentially encode polypeptides with predicted masses of 27.7, 22.3, 11.4, 16.2, 31.3, 8.1, 16.2 and 36.7 kDa, respectively. All eight genes are transcribed from the same strand as hupSL and hupABYCDE. A chroococcum, therefore, has a total of 16 contiguous genes affecting hydrogenase activity beginning with hupS and ending with hupE. The amino acid sequence deduced from hupZ has the characteristics of a b-type cytochrome. Insertion mutagenesis of hupZ resulted in a mutant incapable of supporting O2-dependent H2 oxidation. The deduced amino acid sequence of hupR shares high homology with bacterial rubredoxins. HupZ and HupR may both be involved in transferring electrons from hydrogenase to the electron transport chain. A mutation in hupV knocked out hydrogenase activity entirely; this gene may be involved in processing the large subunit of hydrogenase. It is now clear that the genes controlling [NiFe] hydrogenase activity in many bacteria including Azotobacter chroococcum, Alcaligenes eutrophus, Rhizobium leguminosarum, Rhodobacter capsulatus and Escherichia coli are highly conserved, organized in much the same manner, and likely derived from a common ancestor.
褐球固氮菌的吸氢（Hup）活性取决于一组分布在染色体上13687 bp的基因。该基因簇的六个辅助基因hupABYCDE位于结构基因hupSL下游4.8 kb处，是功能性[NiFe]氢化酶形成所必需的。现已完成hup特异性DNA中间4.8 kb的测序。这揭示了另外八个紧密连锁的开放阅读框，我们将其命名为hupZ、hupM、hupN、hupO、hupQ、hupR、hupT和hupV。这些基因可能分别编码预测分子量为27.7、22.3、11.4、16.2、31.3、8.1、16.2和36.7 kDa的多肽。所有八个基因都与hupSL和hupABYCDE从同一条链转录。因此，褐球固氮菌共有16个连续的基因影响氢化酶活性，从hupS开始到hupE结束。从hupZ推导的氨基酸序列具有b型细胞色素的特征。hupZ的插入诱变产生了一个无法支持依赖O2的H2氧化的突变体。hupR推导的氨基酸序列与细菌红素氧还蛋白具有高度同源性。HupZ和HupR可能都参与将电子从氢化酶转移到电子传递链。hupV中的突变完全消除了氢化酶活性；该基因可能参与氢化酶大亚基的加工。现在很清楚，包括褐球固氮菌、真养产碱菌、豌豆根瘤菌、荚膜红细菌和大肠杆菌在内的许多细菌中控制[NiFe]氢化酶活性的基因高度保守，以大致相同的方式组织，并且可能起源于一个共同的祖先。
