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P. Valentin-Hansen B. Holst J. Josephsen K. Hammer B. Albrechtsen † 《Molecular microbiology》1989,3(10):1385-1390
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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.
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P Gerlach L Sgaard-Andersen H Pedersen J Martinussen P Valentin-Hansen E Bremer 《Journal of bacteriology》1991,173(17):5419-5430
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. 相似文献
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Tandem DNA-bound cAMP-CRP complexes are required for transcriptional repression of the deoP2 promoter by the CytR repressor in Escherichia coli 总被引:8,自引:2,他引:6
L. Sogaard-Andersen N. E. Mellegaard † S. R. Douthwaite P. Valentin-Hansen 《Molecular microbiology》1990,4(9):1595-1601
We have studied the deoP2 promoter in Escherichia coli to define features important for its interaction with the CytR repressor. As is characteristic for CytR-regulated promoters, deoP2 encodes tandem binding sites for the activating complex cAMP-CRP. One of these sites, CRP-1, overlaps the -35 region, and is sufficient for activation; the second site, CRP-2, centred around -93, is indispensable for repression. Here we demonstrate, by means of in vivo titration, that CytR interaction with deoP2 depends not only on CRP-2, but also on CRP-1 and the length and possibly the sequence separating these two sites. Also, point mutations in either CRP site reduce or abolish CytR titration; however, no co-operativity is observed in the interaction of CytR with the two CRP binding sites. Furthermore, the reduction in CytR titration parallels the reduction in binding of cAMP-CRP to the mutated CRP sites in vitro. These observations are not easily explained by current models for the action of prokaryotic repressors; instead we favour a model in which the interaction of CytR with deoP2 depends on the presence of tandem DNA-bound cAMP-CRP complexes. 相似文献
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A simple mechanism for co-dependence on two activators at an Escherichia coli promoter 总被引:7,自引:0,他引:7
Joseph T. Wade Tamara A. Belyaeva Eva I. Hyde Stephen J.W. Busby 《The EMBO journal》2001,20(24):7160-7167