PMID:1715855
| Citation |
Gerlach, P, Søgaard-Andersen, L, Pedersen, H, Martinussen, J, Valentin-Hansen, P and Bremer, E (1991) The cyclic AMP (cAMP)-cAMP receptor protein complex functions both as an activator and as a corepressor at the tsx-p2 promoter of Escherichia coli K-12. J. Bacteriol. 173:5419-30 |
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| Abstract |
The tsx-p2 promoter is one of at least seven Escherichia coli promoters that are activated by the cyclic AMP (cAMP)-cAMP receptor protein (CRP) complex and negatively regulated by the CytR repressor. DNase I footprinting assays were used to study the interactions of these regulatory proteins with the tsx-p2 promoter region and to characterize tsx-p2 regulatory mutants exhibiting an altered response to CytR. We show that the cAMP-CRP activator complex recognizes two sites in tsx-p2 that are separated by 33 bp: a high-affinity site (CRP-1) overlaps the -35 region, and a low-affinity site (CRP-2) is centered around position -74 bp. The CytR repressor protects a DNA segment that is located between the two CRP sites and partially overlaps the CRP-1 target. In combination, the cAMP-CRP and CytR proteins bind cooperatively to tsx-p2, and the nucleoprotein complex formed covers a region of 78 bp extending from the CRP-2 site close to the -10 region. The inducer for the CytR repressor, cytidine, does not prevent in vitro DNA binding of CytR, but releases the repressor from the nucleoprotein complex and leaves the cAMP-CRP activator bound to its two DNA targets. Thus, cytidine interferes with the cooperative DNA binding of cAMP-CRP and CytR to tsx-p2. We characterized four tsx-p2 mutants exhibiting a reduced response to CytR; three carried mutations in the CRP-2 site, and one carried a mutation in the region between CRP-1 and the -10 sequence. Formation of the cAMP-CRP-CytR DNA nucleoprotein complex in vitro was perturbed in each mutant. These data indicate that the CytR repressor relies on the presence of the cAMP-CRP activator complex to regulate tsx-p2 promoter activity and that the formation of an active repression complex requires the combined interactions of cAMP-CRP and CytR at tsx-p2. |
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| Keywords |
Amino Acid Sequence; Bacterial Outer Membrane Proteins/genetics; Bacterial Proteins/metabolism; Base Sequence; Carrier Proteins/metabolism; Cyclic AMP/metabolism; Cyclic AMP Receptor Protein; DNA Fingerprinting; DNA, Bacterial/genetics; DNA, Bacterial/metabolism; DNA-Binding Proteins/metabolism; Escherichia coli/genetics; Escherichia coli Proteins; Genes, Bacterial; Molecular Sequence Data; Mutation; Plasmids; Promoter Regions, Genetic; RNA, Bacterial/analysis; Receptors, Cyclic AMP/metabolism; Receptors, Virus; Regulatory Sequences, Nucleic Acid; Repressor Proteins/genetics; Repressor Proteins/isolation & purification; Repressor Proteins/metabolism |
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