cAMP-CRP repression
E sigma(54) holoenzyme-regulated promoters
loop formation
protein-protein interactions
regulation in E-coli
ENHANCER-BINDING PROTEIN
NITROGEN-FIXATION GENES
CAMP RECEPTOR PROTEIN
ESCHERICHIA-COLI
RHIZOBIUM-MELILOTI
PHOSPHOTRANSFERASE SYSTEM
KLEBSIELLA-PNEUMONIAE
ALPHA-SUBUNIT
CYCLIC-AMP
CENTRAL DOMAIN
The cAMP receptor protein (CRP) is an activator of sigma(70)-dependent transcription, Analysis of the sigma(54)-dependent dctA promoter reveals a novel negative regulatory function for CRP, CRP can bind to two distant sites of the dctA promoter, sites which overlap the upstream activator sequences for the DctD activator, CRP interacts with E sigma(54) bound at the dctA promoter via DNA loop formation, When the CRP-binding sites are deleted, CRP still interacts in a cAMP-dependent manner with the stable E sigma(54) closed complex via protein-protein contacts, CRP is able to repress activation of the dctA promoter, even in the absence of specific CRP-binding sites, CRP affects both the final level and the kinetics of activation, The establishment of the repression and its release by the NtrC activator proceed via slow processes, The kinetics suggest that CRP favours a new form of closed complex which interconverts slowly with the classical closed intermediate, Only the latter is capable of interacting with an activator to form an open promoter complex, Thus, E sigma(54) promoters are responsive to CRP, a protein unrelated to sigma(54) activators, and the repression exerted is the direct result of an interaction between E sigma(54) and the CRP-cAMP complex.