Department of Biophysics and Chemical Biology, Seoul National University, Seoul 151-742, Republic of Korea.
Mol Microbiol. 2010 Dec;78(6):1468-83. doi: 10.1111/j.1365-2958.2010.07419.x. Epub 2010 Oct 15.
An Escherichia coli mutant devoid of enzyme IIA(Ntr) (EIIA(Ntr) ) of the nitrogen PTS is extremely sensitive to leucine-containing peptides due to decreased expression of acetohydroxy acid synthase. This decreased expression is due to defective potassium homeostasis. We further elucidate here the mechanism for regulation of gene expression by the intracellular level of K(+) . The leucine hypersensitivity of a ptsN (encoding EIIA(Ntr) ) mutant was suppressed by deleting rpoS, encoding the stationary phase σ factor. Despite intracellular levels of sigma factors comparable to the wild-type strain, most of the genes downregulated in a ptsN mutant are controlled by σ(70) , while all the upregulated genes are controlled by σ(S) , implying that the balance of sigma activities is modified by ptsN deletion. This change of sigma factor activities in the deletion mutant was found to be due to increased levels of K(+) . In vitro transcription assays demonstrated that a σ(70) controlled gene and a σ(S) controlled gene were differentially affected by potassium concentration. Biochemical studies revealed that K(+) is responsible for sigma factor competition by differentially influencing the binding of σ(70) and σ(S) to core RNA polymerase. Taken together, the data suggest that EIIA(Ntr) controls sigma factor selectivity by regulating the intracellular K(+) level.
一种缺乏氮 PTS 酶 IIA(Ntr)（EIIA(Ntr)）的大肠杆菌突变体由于乙酰羟酸合酶表达降低而对含亮氨酸的肽极其敏感。这种表达降低是由于钾稳态失调所致。我们在这里进一步阐明了细胞内 K(+)水平对基因表达调控的机制。ptsN（编码 EIIA(Ntr)）突变体的亮氨酸敏感性通过删除编码停滞期 σ 因子 rpoS 得到抑制。尽管细胞内 σ 因子的水平与野生型菌株相当，但在 ptsN 突变体中下调的大多数基因受 σ(70)控制，而所有上调的基因都受 σ(S)控制，这表明 σ 活性的平衡通过 ptsN 缺失进行了修饰。在缺失突变体中，σ 因子活性的这种变化被发现是由于 K(+)水平的增加。体外转录实验表明，σ(70)控制的基因和 σ(S)控制的基因受钾浓度的不同影响。生化研究表明，K(+)通过不同地影响 σ(70)和 σ(S)与核心 RNA 聚合酶的结合来竞争 σ 因子。总之，数据表明 EIIA(Ntr)通过调节细胞内 K(+)水平来控制 σ 因子的选择性。
