Bedouelle H
J Mol Biol. 1983 Nov 15;170(4):861-82. doi: 10.1016/s0022-2836(83)80192-2.
The malB region of Escherichia coli is composed of two operons, malEFG and malK-lamB, transcribed divergently from a control region located between the malE and malK genes. Expression of the malB operons is under the positive control of the malT gene product (MalT) and maltose and of the crp gene product (CRP) and cyclic AMP. Strains in which the lac genes have been fused to malE or malK are unable to use lactose as carbon source if they have been deleted for malT or crp. Mutations in the malB region allowing such fusion strains to grow on lactose have been isolated. These and previously isolated mutations were genetically characterized. As regards the malEp promoter mutations, malEp9, malEp1 and malEp6 create new promoters that are MalT and CRP independent. malEp9 and malEp1 change residues -1 and -2, respectively, of malEp without altering its activity. malEp6 duplicates six base-pairs between residues -22 and -23. malEp3 improves the -10 region hexamer. malEp5 deletes residues -29 to -62. It creates a new promoter that is MalT independent, CRP dependent, likely by fusing together functional regions of malEp that are normally apart. malEp5 also reduces the expression of malK-lamB, suggesting the existence of a link between the malEp and malKp promoters. As regards the malKp mutations, malKp6 changes residue -81 of malKp without altering its activity. It creates a new promoter, which is MalT independent, CRP dependent, likely by using a pre-existing cyclic AMP/CRP binding site. malKp102 changes residue -36, two bases upstream of the -35 region hexamer. It decreases the activity of malKp by at least four orders of magnitude and likely alters the MalT binding site. These results are discussed in terms of regulatory interactions within the malB control region.
大肠杆菌的malB区域由两个操纵子，即malEFG和malK-lamB组成，它们从位于malE和malK基因之间的一个控制区域向相反方向转录。malB操纵子的表达受malT基因产物（MalT）以及麦芽糖的正调控，同时也受crp基因产物（CRP）和环腺苷酸的正调控。如果lac基因与malE或malK融合的菌株缺失了malT或crp，那么它们就无法利用乳糖作为碳源。已分离出能使此类融合菌株在乳糖上生长的malB区域突变。对这些以及之前分离出的突变进行了遗传学特征分析。关于malEp启动子突变，malEp9、malEp1和malEp6产生了新的启动子，这些启动子不依赖MalT和CRP。malEp9和malEp1分别改变了malEp的-1和-2位残基，但不改变其活性。malEp6在-22和-23位残基之间重复了六个碱基对。malEp3改善了-10区域的六聚体。malEp5缺失了-29至-62位残基。它产生了一个新的启动子，该启动子不依赖MalT，依赖CRP，可能是通过将通常分开的malEp功能区域融合在一起实现的。malEp5还降低了malK-lamB的表达，这表明malEp和malKp启动子之间存在联系。关于malKp突变，malKp6改变了malKp的-81位残基，但不改变其活性。它产生了一个新的启动子，该启动子不依赖MalT，依赖CRP，可能是通过利用一个预先存在的环腺苷酸/CRP结合位点实现的。malKp102改变了-35区域六聚体上游两个碱基处的-36位残基。它使malKp的活性降低了至少四个数量级，并且可能改变了MalT结合位点。将根据malB控制区域内的调控相互作用对这些结果进行讨论。
