Pawlowski K, Klosse U, de Bruijn F J
Max-Planck-Institut für Züchtungsforschung, Köln, FRG.
Mol Gen Genet. 1991 Dec;231(1):124-38. doi: 10.1007/BF00293830.
Azorhizobium caulinodans ORS571 nifA regulation is partially mediated by the nitrogen regulatory gene ntrC. However, the residual nifA expression in ntrC mutant strains is still modulated by the cellular nitrogen and oxygen status. A second ntrC-homologous region, linked to ntrC, was identified and characterized by site-directed insertion mutagenesis and DNA sequencing. Tn5 insertions in this region cause pleiotropic defects in nitrogen metabolism and affect free-living as well as symbiotic nitrogen fixation. DNA sequencing and complementation studies revealed the existence of a bicistronic operon (ntrYX). NtrY is likely to represent the transmembrane 'sensor' protein element in a two-component regulatory system. NtrX shares a high degree of homology with NtrC proteins of other organisms and probably constitutes the regulator protein element. The regulation of the ntrYX and ntrC loci and the effects of ntrYX, ntrY and ntrX mutations on nifA expression were examined using beta-galactosidase gene fusions. NtrY/NtrX were found to modulate nifA expression and ntrYX transcription was shown to be partially under the control of NtrC.
茎瘤固氮根瘤菌ORS571的nifA调控部分由氮调控基因ntrC介导。然而，ntrC突变菌株中nifA的残留表达仍受细胞氮和氧状态的调节。通过定点插入诱变和DNA测序鉴定并表征了与ntrC相连的第二个ntrC同源区域。该区域的Tn5插入导致氮代谢出现多效性缺陷，并影响自由生活以及共生固氮。DNA测序和互补研究揭示了一个双顺反子操纵子（ntrYX）的存在。NtrY可能代表双组分调节系统中的跨膜“传感器”蛋白元件。NtrX与其他生物体的NtrC蛋白具有高度同源性，可能构成调节蛋白元件。使用β-半乳糖苷酶基因融合研究了ntrYX和ntrC基因座的调控以及ntrYX、ntrY和ntrX突变对nifA表达的影响。发现NtrY/NtrX可调节nifA表达，并且ntrYX转录显示部分受NtrC控制。
