Cyclic AMP receptor protein functions as a repressor of the osmotically inducible promoter proP P1 in Escherichia coli.
Transcription of the proP gene, encoding a transporter of the osmoprotectants proline and glycine betaine, is controlled from two promoters, P1 and P2, that respond primarily to osmotic and stationary-phase signals, respectively. The P1 promoter is normally expressed at a very low level under low or normal medium osmolarity. We demonstrate that the binding of the cyclic AMP (cAMP) receptor protein (CRP) to a site centered at -34.5 within the promoter is responsible for the low promoter activity under these conditions. A brief period of reduced CRP binding in early log phase corresponds to a transient burst of P1 transcription upon resumption of growth in Luria-Bertani broth. A CRP binding-site mutation or the absence of a functional crp gene leads to high constitutive expression of P1. We show that the binding of CRP-cAMP inhibits transcription by purified RNA polymerase in vitro at P1, but this repression is relieved at moderately high potassium glutamate concentrations. Likewise, open-complex formation at P1 in vivo is inhibited by the presence of CRP under low-osmolarity conditions. Because P1 expression can be further induced by osmotic upshifts in a delta crp strain or in the presence of the CRP binding-site mutation, additional controls exist to osmotically regulate P1 expression.
Xu
J
J
Department of Biological Chemistry, UCLA School of Medicine, Los Angeles, California 90095-1737, USA.
Johnson
R C
RC
D001426:Bacterial Proteins / Q000235:genetics*; D002352:Carrier Proteins / Q000235:genetics*; D000242:Cyclic AMP / Q000502:physiology; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D016297:Mutagenesis, Site-Directed; D011401:Promoter Regions, Genetic; D011953:Receptors, Cyclic AMP / Q000502:physiology*; D012097:Repressor Proteins / Q000235:genetics*; D027981:Symporters; D014158:Transcription, Genetic; D014882:Water-Electrolyte Balance
D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; C079244:ProP protein, E coli; D011953:Receptors, Cyclic AMP; D012097:Repressor Proteins; D027981:Symporters; D000242:Cyclic AMP