Milcamps A, Van Dommelen A, Stigter J, Vanderleyden J, de Bruijn F J
MSU-DOE Plant Research Laboratory, Michigan State University, East Lansing 48824, USA.
Can J Microbiol. 1996 May;42(5):467-78. doi: 10.1139/m96-064.
The rpoN (ntrA) gene (encoding sigma 54) of Azospirillum brasilense Sp7 was isolated by using conserved rpoN primers and the polymerase chain reaction, and its nucleotide sequence was determined. The deduced amino acid sequence of the RpoN protein was found to share a high degree of homology with other members of the sigma 54 family. Two additional open reading frames were found in the Azospirillum brasilense rpoN region, with significant similarity to equivalent regions surrounding the rpoN locus in other bacteria. An rpoN mutant of Azospirillum brasilense Sp7 was constructed by gene replacement and found to be defective in nitrogen fixation, nitrate assimilation, and ammonium uptake. Lack of ammonium uptake was also found in previously isolated Azospirillum brasilense ntrB and ntrC mutants, further supporting the role of the ntr system in this process. In addition, the rpoN mutant was found to be nonmotile, suggesting a role of RpoN in Azospirillum brasilense flagellar biosynthesis.
利用保守的rpoN引物和聚合酶链反应，分离出了巴西固氮螺菌Sp7的rpoN（ntrA）基因（编码σ54），并测定了其核苷酸序列。发现RpoN蛋白的推导氨基酸序列与σ54家族的其他成员具有高度同源性。在巴西固氮螺菌rpoN区域发现了另外两个开放阅读框与其他细菌中rpoN基因座周围的等效区域具有显著相似性。通过基因替换构建了巴西固氮螺菌Sp7 的rpoN突变体，发现其在固氮、硝酸盐同化和铵摄取方面存在缺陷。在先前分离的巴西固氮螺菌ntrB和ntrC突变体中也发现了铵摄取缺陷，进一步支持了ntr系统在此过程中的作用。此外，发现rpoN突变体不具有运动性，这表明RpoN在巴西固氮螺菌鞭毛生物合成中发挥作用。
