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首页> 外文期刊>Journal of Molecular Biology >PYRIMIDINE REGULATION OF THE ESCHERICHIA COLI AND SALMONELLA TYPHIMURIUM CARAB OPERONS - CARP AND INTEGRATION HOST FACTOR (IHF) MODULATE THE METHYLATION STATUS OF A GATC SITE PRESENT IN THE CONTROL REGION
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PYRIMIDINE REGULATION OF THE ESCHERICHIA COLI AND SALMONELLA TYPHIMURIUM CARAB OPERONS - CARP AND INTEGRATION HOST FACTOR (IHF) MODULATE THE METHYLATION STATUS OF A GATC SITE PRESENT IN THE CONTROL REGION

机译：大肠埃希氏菌和鼠伤寒沙门氏菌嘧啶的嘧啶调节-鲤鱼和整合寄主因子（IHF）调节了控制区域中存在的GATC部位的甲基化状态

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By measuring the protection against Dam methylase modification of a GATC sequence located 106 bp upstream of the startpoint of promoter P1 in the control region of the carAB operon (encoding carbamoylphosphate synthetase) we have obtained evidence for a direct correlation between the degree of in vivo occupancy of a specific regulatory target site and the repressibility of the P1 promoter by pyrimidine residues. A high uridine nucleotide pool as well as binding of the carP (alias xerB/pepA) gene product and of the integration host factor (IHF) to the carAB control region are prerequisites to observe this in vivo protection, Purified CarP binds in vitro to the carAB control region and protects against DNase I two approximately 25 bp long stretches, one of which is located just downstream of the GATC sequence. Mutations in this site strongly impair the pyrimidine regulation of the P1 promoter and the interference with Dam methylase modification. These processes are also strongly impaired in the absence of integration host factor and in mutants affected in the IHF site located some 200 bp upstream of this Dam methylase modification site. IHF therefore exerts at least part of its antagonistic effects on P1, i.e. increased expression in minimal medium but increased repression in the presence of pyrimidine residues, indirectly by influencing the formation or the stability of a particular protein-DNA complex. Furthermore, we demonstrate that the distance separating the IHF and Dam methylase target sites is crucial for the in vivo protection and for pyrimidine-mediated regulation of the promoter expression. Mutations altering this distance result in severe reductions of the degree of in vivo protection and, concomitantly, of the repressibility by pyrimidine residues of promoter P1 activity in a way indicative of the formation of a complex nucleoprotein structure. Since neither IHF nor CarP require pyrimidine residues to bind to the carAB control region, at least not in vitro, it is tempting to suggest that IHF and CarP-induced bending and looping provide changes in DNA topology that are required for assembling a specific pyrimidine-dependent nucleoprotein complex that modulates P1 activity. [References: 23]
机译：通过测量对carAB操纵子（编码氨基甲酰磷酸合成酶）控制区中启动子P1起点上游106 bp的GATC序列的Dam甲基化修饰的保护作用，我们获得了体内占有率之间直接相关的证据。特定的调控靶位点和嘧啶残基对P1启动子的阻遏性。高尿苷核苷酸池以及carP（别名xerB / pepA）基因产物和整合宿主因子（IHF）与carAB控制区的结合是观察这种体内保护的先决条件，纯化的CarP在体外与该结合物结合。 carAB控制区，可防止DNase I的两个大约25 bp长的延伸，其中之一位于GATC序列的下游。该位点的突变强烈破坏了P1启动子的嘧啶调节，并干扰了Dam甲基化酶的修饰。在没有整合宿主因子的情况下，以及在位于该Dam甲基化酶修饰位点上游约200 bp的IHF位点受影响的突变体中，这些过程也会受到严重损害。因此，IHF至少部分地对P1具有拮抗作用，即通过影响特定蛋白质-DNA复合物的形成或稳定性间接地在基本培养基中增加表达，但在存在嘧啶残基的情况下增加抑制作用。此外，我们证明分隔IHF和Dam甲基化酶靶位点的距离对于体内保护和嘧啶介导的启动子表达调节至关重要。改变该距离的突变导致体内保护程度的严重降低，并伴随着嘧啶残基对启动子P1活性的阻遏性的降低，从而指示了复杂核蛋白结构的形成。由于IHF和CarP都不需要嘧啶残基才能与carAB控制区结合，至少在体外不需要，因此很容易建议IHF和CarP诱导的弯曲和环化可提供组装特定嘧啶-嘧啶所需的DNA拓扑变化。依赖的核蛋白复合物，可调节P1活性。 [参考：23]

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