Premium
Catabolite repression by glucose 6‐phosphate, gluconate and lactose in Escherichia coli
Author(s) -
Hogema Boris M.,
Arents Jos C.,
Inada Toshifumi,
Aiba Hiroji,
Van Dam Karel,
Postma Pieter W.
Publication year - 1997
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.1997.3991761.x
Subject(s) - catabolite repression , psychological repression , fed batch culture , enzyme repression , biology , lactose , biochemistry , camp receptor protein , beta galactosidase , medicine , microbiology and biotechnology , endocrinology , escherichia coli , mutant , gene expression , promoter , gene , fermentation
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 β‐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.