Foster-Hartnett D, Kranz R G
Department of Biology, Washington University, St. Louis, Missouri 63130.
Mol Microbiol. 1992 Apr;6(8):1049-60. doi: 10.1111/j.1365-2958.1992.tb02170.x.
Transcription of Rhodobacter capsulatus genes encoding the nitrogenase polypeptides (nifHDK) is repressed by fixed nitrogen and oxygen. R. capsulatus nifA1 and nifA2 encode identical NIFA proteins that activate transcription of nifHDK and other nif genes. In this study, we report that nifA1-lacZ and nifA2-lacZ fusions are repressed in the presence of NH3 and activated to similar levels under nitrogen-deficient conditions. This nitrogen-controlled activation was dependent on R. capsulatus ntrC (which encodes a transcriptional activator) but not rpoN (which encodes an RNA polymerase sigma factor). We have used primer extension analyses of nifA1, nifA2 and nifH and deletion analyses of nifA1 and nifA2 upstream regions to define likely promoters and cis upstream activation sequences required for nitrogen control of these genes. Primer extension mapping confirmed that ntrC but not rpoN is required for nifA1 and nifA2 activation, and that nifA1 and nifA2 do not possess typical RPON-activated promoters.
编码固氮酶多肽（nifHDK）的荚膜红细菌基因的转录受固定态氮和氧的抑制。荚膜红细菌的nifA1和nifA2编码相同的NIFA蛋白，该蛋白可激活nifHDK和其他nif基因的转录。在本研究中，我们报道nifA1-lacZ和nifA2-lacZ融合基因在有NH3存在时受到抑制，而在缺氮条件下被激活至相似水平。这种氮控制的激活依赖于荚膜红细菌的ntrC（其编码一种转录激活因子），而不依赖于rpoN（其编码一种RNA聚合酶σ因子）。我们利用对nifA1、nifA2和nifH的引物延伸分析以及对nifA1和nifA2上游区域的缺失分析，来确定这些基因的氮控制所需的可能启动子和顺式上游激活序列。引物延伸图谱证实，ntrC而非rpoN是nifA1和nifA2激活所必需的，并且nifA1和nifA2不具有典型的由RPON激活的启动子。
