Ramírez-Arcos S, Fernández-Herrero L A, Berenguer J
Centro de Biología Molecular Severo Ochoa UAM-CSIC Universidad Autónoma de Madrid, Spain.
Biochim Biophys Acta. 1998 Mar 9;1396(2):215-27. doi: 10.1016/s0167-4781(97)00183-8.
T. thermophilus HB8 contains a nitrate reductase gene cluster which is absent from closely related strains. This cluster encodes 4 ORFs (a-d) similar in organization and protein sequence to those encoded by respiratory nitrate reductase operons (narGHJI) of Escherichia coli, Bacillus subtilis, Pseudomonas fluorescens, and Thiosphaera pantothropha. The highest similarity is shown between the proteins encoded by the ORFa, ORFb and ORFd, and the structural components of the mesophilic nitrate reductases NarG (alpha), NarH (beta), and NarI (gamma) proteins, whilst ORFc encodes a protein which showed lower similarity to NarJ, a protein of unknown function encoded between narH and narI genes in all the nar cluster so far sequenced. This T. thermophilus HB8 narGHJI cluster is strongly induced by the combined effect of nitrate and low oxygen concentration, giving rise to the synthesis of an enzyme whose optimal temperature and pH was determined to be 80 degrees C, and pH 10, respectively. We also demonstrate that insertional inactivation of the narG and narH genes of this cluster results in strictly aerobic mutants, showing its sole responsibility in the strain specific ability of T. thermophilus HB8 to grow anaerobically.
嗜热栖热菌HB8含有一个硝酸盐还原酶基因簇，而密切相关的菌株中不存在该基因簇。该基因簇编码4个开放阅读框（a - d），其组织和蛋白质序列与大肠杆菌、枯草芽孢杆菌、荧光假单胞菌和泛养硫球菌的呼吸硝酸盐还原酶操纵子（narGHJI）所编码的相似。ORFa、ORFb和ORFd所编码的蛋白质与嗜温硝酸盐还原酶NarG（α）、NarH（β）和NarI（γ）蛋白的结构成分显示出最高的相似性，而ORFc编码的蛋白质与NarJ的相似性较低，NarJ是迄今为止所有已测序的nar基因簇中位于narH和narI基因之间的一个功能未知的蛋白质。嗜热栖热菌HB8的narGHJI基因簇在硝酸盐和低氧浓度的联合作用下被强烈诱导，从而合成一种酶，其最适温度和pH分别测定为80℃和pH 10。我们还证明，该基因簇的narG和narH基因的插入失活导致严格需氧突变体，表明其对嗜热栖热菌HB8厌氧生长的菌株特异性能力负有唯一责任。
