Surface signaling in transcriptional regulation of the ferric citrate transport system ofEscherichia coli: mutational analysis of the alternative sigma factor FecI supports its essential role infec transport gene transcription
Surface signaling in transcriptional regulation of the ferric citrate transport system ofEscherichia coli: mutational analysis of the alternative sigma factor FecI supports its essential role infec transport gene transcription
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大肠杆菌柠檬酸铁转运系统转录调控中的表面信号传导：替代 Sigma 因子 FecI 的突变分析支持其在 fec 转运基因转录中的重要作用
DOI：
10.1007/bf02174034
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发表时间：
1996
期刊：
影响因子：
--
通讯作者：
Volkmar Braun
中科院分区：
文献类型：
--
作者：
Martina Ochs;A. Angerer;S. Enz;Volkmar Braun
在大肠杆菌中，柠檬酸铁通过与外膜受体蛋白FecA结合而不进入细胞，诱导柠檬酸铁转运基因（fec）的转录。柠檬酸铁引起的信号通过TonB、ExbB和ExbD穿过外膜。FecR通过细胞质膜传递信号并激活位于细胞质中的FecI。FecI属于响应于细胞质外刺激的σ因子的亚组。感染产生染色体插入和缺失突变;所产生的突变体完全缺乏FecA的生产和fecB-lacZ的表达。铁饥饿不能降低铁转运基因转录的抑制。在预测的螺旋-转角-螺旋FecI基序中产生错义点突变，以检查其在转录起始中的作用。丙氨酸（E141 A）在第一螺旋的第三位的谷氨酸的替代减少了在没有柠檬酸铁的情况下的FecI的剩余活性的野生型水平的30%，但inducedfec转录几乎正常的柠檬酸铁的存在下。突变体FecI（K145 E）显示156%的野生型FecI在柠檬酸铁的情况下的活性，并赋予柠檬酸铁的完全诱导。突变体FecI（K155 E），其中有一个突变的第二个螺旋，在柠檬酸铁的存在下，野生型活性的9%和78%的柠檬酸铁的情况下。体外细胞裂解物DNA结合试验也显示FecI（K155 E）活性降低;在凝胶阻滞实验中，FecI（K155 E）降低了含有fecA启动子的DNA的电泳迁移率，低于野生型FecI。fecI不受自身调节，体内缺乏FecI诱导的fecI-lacZ表达和体外缺乏特异性fecI转录。相反，ecI mRNA的形成需要σ70。我们的结论是fec转运基因的转录受FecI的调控，而FecI通过FecR对柠檬酸铁起反应，fecI和fecR的共转录受Fur阻遏物的抑制，从而导致fec转运基因的低水平转录。
Ferric citrate induces transcription of the ferric citrate transport genes (fec) inEscherichia coli by binding to the outer membrane receptor protein FecA without entering the cell. The signal elicited by ferric citrate crosses the outer membrane via TonB, ExbB, and ExbD. FecR transmits the signal across the cytoplasmic membrane and activates FecI located in the cytoplasm. FecI belongs to a subgroup of sigma factors that respond to extracytoplasmic stimuli. Chromosomal insertion and deletion mutations were generated infecI; the resulting mutants were totally devoid of FecA production andfecB-lacZ expression. Iron starvation did not derepressfec transport gene transcription infecI mutants. Missense point mutations were generated in the predicted helix-turn-helix motif of FecI to examine its role in transcription initiation. Replacement of glutamate by alanine (E141A) at the third position in the first helix reduced the residual activity of FecI in the absence of ferric citrate to 30% of the wild-type level, but inducedfec transcription almost normally in the presence of ferric citrate. Mutant FecI(K145E) displayed 156% of the activity of wild-type FecI in the absence of ferric citrate and conferred full induction by ferric citrate. Mutant FecI(K155E), which has a mutation in the second helix, showed 9% of the wild-type activity in the presence of ferric citrate and 78% in the absence of ferric citrate. The reduced activity of FecI(K155E) was also shown in vitro by DNA binding assays with cell lysates; in gel retardation experiments FecI(K155E) reduced the electrophoretic mobility offecA promoter-containing DNA less than did wild-type FecI.fecI is not autoregulated, as demonstrated by the lack of FecI-inducedfecI-lacZ expression in vivo and by the lack of specificfecI transcription in vitro. Instead, formation offecI mRNA requires σ70. We conclude that transcription of thefec transport genes is regulated by FecI, which responds to ferric citrate via FecR.fecI andfecR cotranscription is inhibited by the iron-loaded Fur repressor, which then results in a low level of transcription of thefec transport genes.
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DOI：
10.1073/pnas.82.4.1074
发表时间：
1985-01-01
影响因子：
11.1
作者：
TABOR, S;RICHARDSON, CC
通讯作者：
RICHARDSON, CC
影响因子：
5.6
作者：
SIEGELE, DA;HU, JC;GROSS, CA
通讯作者：
GROSS, CA
影响因子：
5.6
作者：
GARDELLA, T;MOYLE, H;SUSSKIND, MM
通讯作者：
SUSSKIND, MM
DOI：
10.1073/pnas.91.16.7573
发表时间：
1994-08-02
影响因子：
11.1
作者：
LONETTO, MA;BROWN, KL;BUTTNER, MJ
通讯作者：
BUTTNER, MJ