GENETIC CONTROL OF NITRATE RESPIRATION IN E COLI

肠杆菌是兼性需氧菌，当在缺氧条件下培养时，可以使用各种替代的呼吸氧化剂。硝酸盐和亚硝酸盐是首选的替代品，呼吸酶基因表达受到严格控制，以响应它们的可用性。这种控制是由双重相互作用的双组分调节系统介导的。硝酸盐和亚硝酸盐控制两种细胞质膜传感器激酶NarX和NarQ的自磷酸化，然后使两种反应调节因子NarL和NarP磷酸化。磷酸化的反应调节因子与目标操纵子控制区的DNA结合。因此，转录起始根据硝酸盐和亚硝酸盐的可用性被激活或抑制。同源双组分系统控制着不同细菌种类的各种其他过程。Nar调控系统显示出几个可以进行实验研究的复杂性，包括(1)结构相关配体的差异识别；(2)影响激酶和磷酸酶反应的不同传感器-调节器相互作用；(3) DNA结合位点排列的差异性识别；(4)不同靶控制区的差异转录激活。拟议的实验将采用体内和体外方法来探测控制这些差异的特异性决定因素。结果将拓宽我们对双组分信号转导的理解。他们还将加强我们对肠杆菌厌氧生理复杂性的认识，这与理解肠杆菌病原体如肠致病性大肠杆菌、志贺氏菌和沙门氏菌在它们的厌氧栖息地——哺乳动物肠道中的生理有关。

Enterobacteria are facultative aerobes, and when cultured in the absence of oxygen can use a variety of alternative respiratory oxidants. Nitrate and nitrite are the preferred alternatives, and respiratory enzyme gene expression is tightly controlled in response to their availability. This control is mediated by dual interacting two-component regulatory systems. Nitrate and nitrite control the autophosphorylation of two cytoplasmic membrane sensor-kinases, NarX and NarQ, which then phosphorylate two response regulators, NarL and NarP. The phosphorylated response regulators bind to DNA in target operon control regions. Thus, transcription initiation is activated or repressed according to nitrate and nitrite availability. Homologous two-component systems control a variety of other processes in diverse bacterial species. The Nar regulatory system exhibits several complexities that are amenable to experimental investigation, including (1) differential recognition of structurally-related ligands; (2) differential sensor-regulator interactions that influence both kinase and phosphatase reactions; (3) differential recognition of DNA binding site arrangement; and (4) differential transcription activation at different target control regions. Proposed experiments will employ both in vivo and in vitro approaches to probe specificity determinants that control these differences. Results will broaden our understanding of two-component signal transduction. They will also strengthen our appreciation for the complexities of enterobacterial anaerobic physiology, which is relevant to understanding the physiology of enterobacterial pathogens such as enteropathogenic E. coli, Shigella spp. and Salmonella spp. in their anaerobic habitat, the mammalian intestine.