TY - JOUR
T1 - Mechanism responsible for glucose-lactose diauxie in Escherichia coli
T2 - Challenge to the cAMP model
AU - Inada, Toshifumi
AU - Kimata, Keiko
AU - Aiba, Hiroji
N1 - Publisher Copyright:
© Blackwell Science Ltd.
PY - 1996
Y1 - 1996
N2 - Background: The inhibition of β-galactosidase expression in glucose-lactose diauxie is a typical example of the glucose effect in Escherichia coli. It is generally believed that glucose exerts its effect at least partly by reducing the intracellular cAMP level. However, there is no direct evidence that the inhibitory effect of glucose on the expression of the lac operon is mediated by a reduction of the cAMP level in the glucose-lactose system. Results: To examine the roles of cAMP and the cAMP receptor protein (CRP) in the glucose effect, the intracellular levels of these factors were determined during diauxic growth in a glucose-lactose medium. We found that the levels of cAMP and CRP in a lactose-grown phase were not higher than those in a glucose-grown phase, although the cAMP levels increased transiently during the lag phase. The addition of exogenous cAMP eliminated diauxic growth but did not eliminate glucose repression. Glucose repression and diauxie were observed in cells which lack cAMP but produce a cAMP-independent CRP. In addition, inactivation of the lac repressor by the disruption of the lacI gene or the addition of IPTG, eliminated glucose repression. Conclusion: We conclude that the repression of β-galactosidase expression by glucose is not due to the reduction of the cAMP-CRP level but due to an inducer exclusion mechanism which is mediated by the phosphoenolpyruvate-dependent sugar phosphotransferase system.
AB - Background: The inhibition of β-galactosidase expression in glucose-lactose diauxie is a typical example of the glucose effect in Escherichia coli. It is generally believed that glucose exerts its effect at least partly by reducing the intracellular cAMP level. However, there is no direct evidence that the inhibitory effect of glucose on the expression of the lac operon is mediated by a reduction of the cAMP level in the glucose-lactose system. Results: To examine the roles of cAMP and the cAMP receptor protein (CRP) in the glucose effect, the intracellular levels of these factors were determined during diauxic growth in a glucose-lactose medium. We found that the levels of cAMP and CRP in a lactose-grown phase were not higher than those in a glucose-grown phase, although the cAMP levels increased transiently during the lag phase. The addition of exogenous cAMP eliminated diauxic growth but did not eliminate glucose repression. Glucose repression and diauxie were observed in cells which lack cAMP but produce a cAMP-independent CRP. In addition, inactivation of the lac repressor by the disruption of the lacI gene or the addition of IPTG, eliminated glucose repression. Conclusion: We conclude that the repression of β-galactosidase expression by glucose is not due to the reduction of the cAMP-CRP level but due to an inducer exclusion mechanism which is mediated by the phosphoenolpyruvate-dependent sugar phosphotransferase system.
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U2 - 10.1046/j.1365-2443.1996.24025.x
DO - 10.1046/j.1365-2443.1996.24025.x
M3 - Article
C2 - 9133663
AN - SCOPUS:0030089476
VL - 1
SP - 293
EP - 301
JO - Genes to Cells
JF - Genes to Cells
SN - 1356-9597
IS - 3
ER -