Participation of Regulator AscG of the β-Glucoside Utilization Operon in Regulation of the Propionate Catabolism Operon
Participation of Regulator AscG of the β-Glucoside Utilization Operon in Regulation of the Propionate Catabolism Operon
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DOI：
10.1128/jb.00663-09
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发表时间：
2009-10-01
影响因子：
3.2
通讯作者：
Ishihama, Akira
中科院分区：
文献类型：
--
作者：
Ishida, Yuji;Kori, Ayako;Ishihama, Akira
大肠杆菌asc操纵子是利用β - d -半乳糖苷作为碳源的一个隐性遗传系统。负责β - d -半乳糖苷转运和分解代谢的ascFB基因受到AscG调节因子的抑制。经过基因组SELEX筛选，发现AscG识别并结合共识回文序列TGAAACC-GGTTTCA。在ascFB启动子上游的两个位点和丙酸分解代谢的probc操纵子上游的三个位点检测到AscG结合。在AscG中断突变体中，ascFB的转录增强，与AscG的抑制因子模型一致。这种抑制被认为是由于环AMP-CRP与CRP盒子的结合受到干扰，这与ascg结合位点1重叠，以及RNA聚合酶与启动子的结合受到干扰。在大肠杆菌在富培养基中稳定生长的条件下，AscG在细胞内的水平保持在一个可能导致ascFB操纵子被严格抑制的水平。编码prpBCDE激活因子的prpR水平在缺乏AscG的情况下也增加，表明AscG参与了对prpR的抑制。综上所述，这些数据表明通过asc和prp操作子之间的相互作用存在代谢联系。
The asc operon of Escherichia coli is one of the cryptic genetic systems for beta-D-galactoside utilization as a carbon source. The ascFB genes for beta-D-galactoside transport and catabolism are repressed by the AscG regulator. After genomic SELEX screening, AscG was found to recognize and bind the consensus palindromic sequence TGAAACC-GGTTTCA. AscG binding was detected at two sites upstream of the ascFB promoter and at three sites upstream of the prpBC operon for propionate catabolism. In an ascG-disrupted mutant, transcription of ascFB was enhanced, in agreement with the repressor model of AscG. This repression was indicated to be due to interference of binding of cyclic AMP-CRP to the CRP box, which overlaps with the AscG-binding site 1, as well as binding of RNA polymerase to the promoter. Under conditions of steady-state E. coli growth in a rich medium, the intracellular level of AscG stayed constant at a level supposedly leading to tight repression of the ascFB operon. The level of prpR, encoding the activator of prpBCDE, was also increased in the absence of AscG, indicating the involvement of AscG in repression of prpR. Taken together, these data suggest a metabolic link through interplay between the asc and prp operons.