Catabolite repression by glucose 6-phosphate, gluconate and lactose in Escherichia coli
Catabolite repression by glucose 6-phosphate, gluconate and lactose in Escherichia coli
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DOI：
10.1046/j.1365-2958.1997.3991761.x
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发表时间：
1997-05-01
影响因子：
3.6
通讯作者：
Postma, PW
中科院分区：
文献类型：
--
作者：
Hogema, BM;Arents, JC;Postma, PW
虽然葡萄糖对分解代谢物的抑制已被广泛研究，并在肠杆菌科中得到了详细的了解，但不通过磷酸转移酶系统（PTS）运输的碳水化合物对分解代谢物的抑制一直是一个谜。在大肠杆菌中引起分解代谢物抑制的非PTS碳水化合物的例子是葡萄糖酸盐、乳糖和葡萄糖6-磷酸。在这篇文章表明，酶IIA（Glc）的PTS不参与这些碳源分解代谢物的抑制。碳源引起强烈的分解代谢物抑制β -半乳糖苷酶降低了cAMP和cAMP受体蛋白（CRP）的浓度。在cAMP和CRP的数量和抑制强度之间发现了很强的相关性。cAMP和CRP的水平以不同的方式调节。CRP的过量产生和cAMP浓度的升高都不能完全缓解葡萄糖- 6-磷酸、乳糖和葡萄糖酸盐的抑制作用。同时增加cAMP和CRP水平对细胞是致命的。在表达等量camp非依赖性CRP*蛋白的突变体中，分解代谢物抑制缺失。在lac转录独立于cAMP/CRP的突变体中也发现了同样的情况。这些结果，结合6-磷酸葡萄糖、乳糖和葡萄糖酸盐降低cAMP和CRP水平的事实，可以得出结论，cAMP和CRP水平的降低是这些非pts碳源抑制分解代谢的原因。
While catabolite repression by glucose has been studied extensively and is understood in large detail in Enterobacteriaceae, catabolite repression by carbohydrates that are not transported by the phosphotransferase system (PTS) has always remained an enigma, Examples of non-PTS carbohydrates that cause catabolite repression in Escherichia coli are gluconate, lactose and glucose 6-phosphate. In this article it is shown that enzyme IIA(Glc) of the PTS is not involved in catabolite repression by these carbon sources. Carbon sources that caused strong catabolite repression of beta-galactosidase lowered the concentration of both cAMP and the cAMP receptor protein (CRP). A strong correlation was found between the amounts of cAMP and CRP and the strength of the repression. The levels of cAMP and CRP were modulated in various ways. Neither overproduction of CRP nor an increased cAMP concentration could completely relieve the repression by glucose 6-phosphate, lactose and gluconate. Simultaneously increasing the cAMP and the CRP levels was lethal for the cells. In a mutant expressing a constant amount of cAMP-independent CRP* protein, catabolite repression was absent. The same was found in a mutant in which lac transcription is independent of cAMP/CRP. These results, combined with the fact that both the cAMP and the CRP levels are lowered by glucose 6-phosphate, lactose and gluconate, lead to the conclusion that the decreased cAMP and CRP levels are the cause of catabolite repression by these non-PTS carbon sources.