Chapon C
J Bacteriol. 1982 May;150(2):722-9. doi: 10.1128/jb.150.2.722-729.1982.
The maltose regulon consists of three operons controlled by a positive regulatory gene, malT. Deletions of the gene crp were introduced into strains which carried a malT-lacZ hybrid gene. From the observed reduction in beta-galactosidase activity it was concluded that the expression of malT-lacZ, and therefore of malT, is controlled by the catabolite activator protein (CAP), the product of the gene crp. Mutations were obtained which allowed a malT-lacZ hybrid gene to be expressed at a high level even in the absence of CAP. These mutations were shown to be located in or close to the promoter of the malT gene and were called malTp. The malTp mutations were transferred in the cis position to a wild-type malT gene. In the resulting strains, the expression of two of the maltose operons, malEFG and malK-lamB, still required the action of CAP, whereas that of the third operon, malPQ, was CAP independent. Therefore, in wild-type cells, CAP appears to control malPQ expression mainly, if not solely, by regulating the concentration of MalT protein in the cell. On the other hand, it controls the other two operons more stringently, both by regulating malT expression and by a more direct action, probably exerted in the promoters of these operons.
麦芽糖调节子由三个受正调控基因malT控制的操纵子组成。将crp基因的缺失引入携带malT - lacZ杂交基因的菌株中。从观察到的β - 半乳糖苷酶活性降低得出结论，malT - lacZ以及malT的表达受分解代谢物激活蛋白（CAP）控制，CAP是crp基因的产物。获得了一些突变，这些突变使得即使在没有CAP的情况下，malT - lacZ杂交基因也能高水平表达。这些突变被证明位于malT基因的启动子内或其附近，被称为malTp。malTp突变以顺式位置转移到野生型malT基因上。在所得菌株中，两个麦芽糖操纵子malEFG和malK - lamB的表达仍然需要CAP的作用，而第三个操纵子malPQ的表达则不依赖于CAP。因此，在野生型细胞中，CAP似乎主要（如果不是唯一的话）通过调节细胞中MalT蛋白的浓度来控制malPQ的表达。另一方面，它通过调节malT的表达以及可能在这些操纵子的启动子中发挥更直接的作用，更严格地控制另外两个操纵子。
