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首页> 外文期刊>Journal of Molecular Biology >Regulation of the Escherichia coli Allantoin Regulon: Coordinated Function of the Repressor AllR and the Activator AllS.
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Regulation of the Escherichia coli Allantoin Regulon: Coordinated Function of the Repressor AllR and the Activator AllS.

机译：大肠杆菌尿囊素调节子的调控：阻遏物AllR和激活物AllS的协调功能。

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The allantoin regulon of Escherichia coli, formed by three operons expressed from promoters allA(P), gcl(P) and allD(P), is involved in the anaerobic utilization of allantoin as nitrogen source. The expression of these operons is under the control of the repressor AllR. The hyperinduction of one of these promoters (allD(P)) by allantoin in an AllR defective mutant suggested the action of another regulator, presumably of activator type. In this work we have identified ybbS (proposed gene name allS), divergently transcribed from allA, as the gene encoding this activator. Analysis of the expression of the three structural operons in DeltaallS mutant showed that the expression from allD(P) was abolished, suggesting that AllS is essential for the expression of the corresponding operon. In a wild-type strain expression of allS takes place mainly anaerobically and is hyperinduced when the nitrogen source limits growth. However, expression of allS is independent of regulators of the Ntr response, NtrC or Nac. Band shift experiments showed that AllR binds to DNA containing the allS-allA intergenic region and the gcl(P) promoter and its binding is abolished by glyoxylate. Both DNA fragments contain a highly conserved inverted repeat, which after site-directed mutagenesis, has been proven to be the AllR-binding site. This site displays similarity with the IclR family recognized consensus. Interaction of AllR with the single operator present in the allS-allA intergenic region prevented binding of RNA polymerase to either of the two divergent promoters. The regulator AllS interacts only with allD(P) even in the absence of allantoin. Analysis of this promoter allowed us to identify an inverted repeat as a motif for AllS binding. We propose a model for the coordinate control of the allantoin regulon by AllR and AllS.
机译：大肠杆菌的尿囊素调节子由启动子allA（P），gcl（P）和allD（P）表达的三个操纵子组成，参与尿囊素作为氮源的厌氧利用。这些操纵子的表达受阻遏物AllR的控制。尿囊素在AllR缺陷型突变体中对这些启动子之一（allD（P））的过度诱导提示了另一种调节剂（可能是激活剂类型）的作用。在这项工作中，我们确定了从allA转录而来的ybbS（拟议的基因名称allS）是编码该激活因子的基因。分析DeltaallS突变体中三个结构操纵子的表达，结果表明allD（P）的表达被取消，这表明AllS对于表达相应操纵子至关重要。在野生型菌株中，allS的表达主要在厌氧条件下发生，当氮源限制其生长时会过度诱导。但是，allS的表达独立于Ntr反应，NtrC或Nac的调节子。带移实验表明，AllR与包含allS-allA基因间区域和gcl（P）启动子的DNA结合，并且其结合被乙醛酸消除。这两个DNA片段均含有高度保守的反向重复序列，经定点诱变后，该序列已被证明是AllR结合位点。该网站与IclR家庭公认的共识相似。 AllR与allS-allA基因间区域中存在的单个操纵基因的相互作用阻止了RNA聚合酶与两个不同启动子中的一个的结合。即使在没有尿囊素的情况下，调节剂AllS也仅与allD（P）相互作用。对该启动子的分析使我们能够鉴定出反向重复序列作为AllS结合的基序。我们提出了一个模型，用于AllR和AllS对尿囊素调节剂的坐标控制。

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