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Journal of Bacteriology, October 2009, p. 6094-6104, Vol. 191, No. 19
0021-9193/09/$08.00+0     doi:10.1128/JB.00672-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Downregulation of the Escherichia coli guaB Promoter by Upstream-Bound Cyclic AMP Receptor Protein{triangledown} ,{dagger}

Seyyed I. Husnain,1,{ddagger} Stephen J. W. Busby,2 and Mark S. Thomas1*

School of Medicine and Biomedical Sciences, University of Sheffield, Beech Hill Road, Sheffield S10 2RX, United Kingdom,1 School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom2

Received 22 May 2009/ Accepted 17 July 2009

The Escherichia coli guaB promoter (PguaB) is responsible for directing transcription of the guaB and guaA genes, which specify the biosynthesis of the nucleotide GMP. PguaB is subject to growth rate-dependent control (GRDC) and possesses an UP element that is required for this regulation. In addition, PguaB contains a discriminator, three binding sites for the nucleoid-associated protein FIS, and putative binding sites for the regulatory proteins DnaA, PurR, and cyclic AMP receptor protein (CRP). Here we show that the CRP-cyclic AMP (cAMP) complex binds to a site located over 100 bp upstream of the guaB transcription start site, where it serves to downregulate PguaB. The CRP-mediated repression of PguaB activity increases in media that support lower growth rates. Inactivation of the crp or cyaA gene or ablation/translocation of the CRP site relieves repression by CRP and results in a loss of GRDC of PguaB. Thus, GRDC of PguaB involves a progressive increase in CRP-mediated repression of the promoter as the growth rate decreases. Our results also suggest that the CRP-cAMP complex does not direct GRDC at PguaB and that at least one other regulatory factor is required for conferring GRDC on this promoter. However, PurR and DnaA are not required for this regulatory mechanism.

* Corresponding author. Mailing address: School of Medicine and Biomedical Sciences, University of Sheffield, Beech Hill Road, Sheffield S10 2RX, United Kingdom. Phone: 44 (0)114 2712834. Fax: 44 (0)114 2713892. E-mail: m.s.thomas{at}shef.ac.uk

{triangledown} Published ahead of print on 24 July 2009.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

{ddagger} Present address: Department of Microbiology and Molecular Genetics, University of Texas Medical School, 6431 Fannin Street, Houston, TX 77030.

Journal of Bacteriology, October 2009, p. 6094-6104, Vol. 191, No. 19
0021-9193/09/$08.00+0     doi:10.1128/JB.00672-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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