Cava Felipe, Laptenko Oleg, Borukhov Sergei, Chahlafi Zahra, Blas-Galindo Emilio, Gómez-Puertas Paulino, Berenguer José
Centro de Biología Molecular Severo Ochoa, Departamento de Biología Molecular, Universidad Autónoma de Madrid, Madrid 28049, Spain.
Mol Microbiol. 2007 May;64(3):630-46. doi: 10.1111/j.1365-2958.2007.05687.x.
The strains of Thermus thermophilus that contain the nitrate respiration conjugative element (NCE) replace their aerobic respiratory chain by an anaerobic counterpart made of the Nrc-NADH dehydrogenase and the Nar-nitrate reductase in response to nitrate and oxygen depletion. This replacement depends on DnrS and DnrT, two homologues to sensory transcription factors encoded in a bicistronic operon by the NCE. DnrS is an oxygen-sensitive protein required in vivo to activate transcription on its own dnr promoter and on that of the nar operon, but not required for the expression of the nrc operon. In contrast, DnrT is required for the transcription of these three operons and also for the repression of nqo, the operon that encodes the major respiratory NADH dehydrogenase expressed during aerobic growth. Thermophilic in vitro assays revealed that low DnrT concentrations allows the recruitment of the T. thermophilus RNA polymerase sigma(A) holoenzyme to the nrc promoter and its transcription, whereas higher DnrT concentrations are required to repress transcription on the nqo promoter. In conclusion, our data show a complex autoinducible mechanism by which DnrT functions as the transcriptional switch that allows the NCE to take the control of the respiratory metabolism of its host during adaptation to anaerobic growth.
嗜热栖热菌中含有硝酸盐呼吸接合元件（NCE）的菌株，在硝酸盐和氧气耗尽时，会用由Nrc-NADH脱氢酶和Nar-硝酸盐还原酶组成的厌氧呼吸链取代其好氧呼吸链。这种取代取决于DnrS和DnrT，它们是NCE在一个双顺反子操纵子中编码的感觉转录因子的两个同源物。DnrS是一种对氧气敏感的蛋白质，在体内是激活其自身dnr启动子和nar操纵子启动子转录所必需的，但不是nrc操纵子表达所必需的。相比之下，DnrT是这三个操纵子转录所必需的，也是对nqo（编码在好氧生长期间表达的主要呼吸NADH脱氢酶的操纵子）进行抑制所必需的。嗜热体外试验表明，低浓度的DnrT能使嗜热栖热菌RNA聚合酶σ(A)全酶募集到nrc启动子并进行转录，而抑制nqo启动子的转录则需要更高浓度的DnrT。总之，我们的数据显示了一种复杂的自诱导机制，通过该机制，DnrT作为转录开关，使NCE在适应厌氧生长过程中能够控制其宿主的呼吸代谢。
