Abstract:

The positive regulator protein NifA activates the expression of nitrogen fixation (nif) genes in many diazotrophs. Sequence analysis shows that a crucial tyrosine residue in region C6 of NifA protein is highly conserved (Y370 in Pseudomonas stutzeri A1501). β-galactosidase activity analysis showed that Y370C mutant could neither activate the expression of nifH, nor restore nitrogenase activity of NifA deletion mutant strain A1506, while the wild type stain could do so. It was demonstrated that Y370 in NifA protein was critical for the transcriptional activation of nif genes in Pseudomonas stutzeri A1501, and the mechanism needed further investigation.

Key words: Pseudomonas stutzeri A1501, NifA; , site-directed mutagenesis, transcriptional activation

摘要：

NifA为固氮微生物固氮基因(nif)表达的正调控因子，序列分析显示NifA蛋白C6区的一个酪氨酸残基高度保守（对应于A1501为Y370）。β-半乳糖苷酶活性分析表Y370C突变体不能激活nifH启动子，也不能使NifA缺失突变株A1506恢复固氮酶活，而野生型NifA可以激活PnifH+lacZ的表达，并恢复A1506的固氮酶活。研究证明斯氏假单胞菌A1501 NifA蛋白的C6区的Y370氨基酸是NifA蛋白激活nif基因转录的关键位点之一，其具体作用机制值得进一步深入研究。

关键词: 斯氏假单胞菌A1501, NifA蛋白, 定点突变, 转录激活