Wu Guanghui, Hill Susan, Kelly Mark J S, Sawers Gary, Poole Robert K
The Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, The University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, UK.
Nitrogen Fixation Laboratory, John Innes Centre, Colney, Norwich NR4 7UH, UK.
Microbiology (Reading). 1997 Jul;143 ( Pt 7):2197-2207. doi: 10.1099/00221287-143-7-2197.
The cytochrome bd complex in the obligately aerobic diazotroph Azotobacter vinelandii is an oxidase, which, in vivo, has a low affinity for oxygen and is required for respiratory protection of nitrogenase. Mutations caused by insertion of Tn5-B20 upstream of the structural genes (cydAB) for cytochrome bd result in over-expression of this oxidase and, for unexplained reasons, inability of the organism to grow microaerobically. Cloning and sequencing of this upstream region revealed a gene, cydR. The deduced amino acid sequence of CydR indicates that it is a new member of the Fnr Class of regulators and that it represses cydAB expression. Refined mapping data for three insertions in cydR are presented. The cloned cydR gene complemented anaerobic growth of Escherichia coli fnr mutants and strongly enhanced expression of a narG-lacZ fusion in an E. coli fnr mutant.
专性需氧固氮菌维涅兰德固氮菌中的细胞色素bd复合物是一种氧化酶，在体内对氧气亲和力较低，是固氮酶呼吸保护所必需的。在细胞色素bd结构基因（cydAB）上游插入Tn5-B20导致的突变会使这种氧化酶过度表达，且由于不明原因，该生物体无法在微需氧条件下生长。对该上游区域进行克隆和测序发现了一个基因cydR。CydR推导的氨基酸序列表明它是Fnr类调节因子的新成员，并且它会抑制cydAB的表达。本文给出了cydR中三个插入片段的精细定位数据。克隆的cydR基因补充了大肠杆菌fnr突变体的厌氧生长，并强烈增强了大肠杆菌fnr突变体中narG-lacZ融合基因的表达。
