Regulation of expression of the crp gene of Escherichia coli K-12: in vivo study

Abstract

Expression of the crp gene was studied in vivo by use of a crp-lacZ gene fusion first constructed on a plasmid and then transferred onto the chromosome. Our in vivo data confirm the in vitro findings that crp is negatively autoregulated via the cyclic AMP-catabolite gene activator protein complex. We present evidence that gene crp is repressed by glucose.

A lowered concentration of cAMP receptor protein caused by glucose is an important determinant for catabolite repression in Escherichia coli

“…It is interesting to note that the expression of a crp-tac protein fusion was shown to be moderately repressed by glucose (Cossart and Gicquel-Sanzey, 1985). Our finding is consistent with this gene fusion study.…”

“…Beta-galactosidase activity is expressed in Miller units (Miller, 1972), an important contributory factor in the modulation of catabolite repression. Although this assumption is in conflict with early reports suggesting that expression of CRP is constitutive regardless of growth conditions (Guiso and Blazy, 1980;Guiso etai, 1982), recent studies revealed that the regulation of crp transcription is complicated (Aiba, 1983;Cossart and Gicquel-Sanzey, 1985;Okamoto and Freundlich, 1986;Hanamura and Aiba, 1991;1992). This raised the possibility that the level of CRP could vary depending on growth conditions.…”

Cyclic AMP in prokaryotes.

“…CRP-cAMP complex represses the expression of the crp gene itself (4, 66). In contrast to the mechanism involved in CRP-mediated repression of cyaP2 and galP2, CRP-mediated repression of the crp occurs through an indirect mechanism.…”

A new aspect of transcriptional control of the Escherichia coli crp gene: positive autoregulation

“…Based on in vitro studies of the cloned crp gene, we found previously that the transcription of crp is negatively regulated by CRP-cAMP that binds to a specific site {CRP site I) located about 40 bp downstream from the transcription start site {Aiba, 1983). This negative autoreguiation was shown to be operating in vivo by crp-iac fusion studies (Garges and Adhya, 1983;Cossart and Gicquel-Sanzey, 1985), Evidence for the negative autoreguiation of crp in vivo was aiso presented by quantitative analyses of crp mRNA {Okamoto and Freundlich, 1986) and CRP protein (Okamoto et ai.. 1988) in cells harbouring a multicopy crp plasmid. Furthermore, it was shown that the negative autoreguiation of crp was coupled with the activation of a second divergent promoter by CRP-cAMP bound to CRP site i (Okamoto and Freundlich, 1986).…”