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Journal of Bacteriology, November 2003, p. 6624-6632, Vol. 185, No. 22
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.22.6624-6632.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

SoxRS-Regulated Expression and Genetic Analysis of the yggX Gene of Escherichia coli

Pablo J. Pomposiello,1* Anastasia Koutsolioutsou,2 Daniel Carrasco,1 and Bruce Demple2

Department of Microbiology, University of Massachusetts, Amherst, Massachusetts 01003,1 Department of Cancer Cell Biology, Harvard School of Public Health, Boston, Massachusetts 022152

Received 21 March 2003/ Accepted 12 August 2003

Genomic studies with bacteria have identified redox-responsive genes without known roles in counteracting oxidative damage. Previous transcriptional profiling showed that expression of one such gene, yggX, was activated by superoxide stress in Escherichia coli. Here we show that this activation could be mimicked by artificial expression of the regulatory protein SoxS. Northern analysis confirmed the transcriptional activation of yggX by oxidative stress or SoxS expression but not in response to the related MarA or Rob proteins. Northern analysis showed that mltC, which codes for a peptidoglycan hydrolase and is positioned immediately downstream of yggX, was also regulated by oxidative stress or ectopic expression of SoxS. Purified SoxS protein bound to the predicted yggX promoter region, between positions 223 and 163 upstream from the yggX translational start site. Within this region, a 20-bp sequence was found to be necessary for oxidative stress-mediated activation of yggX transcription. A yggX deletion strain was hypersensitive to the redox-cycling agent paraquat, and a plasmid expressing YggX complemented the sensitivity of the deletion strain. Under exposure to paraquat, the yggX deletion strain showed a deficiency in aconitase activity compared to the isogenic wild-type strain, while expression of YggX from a multicopy plasmid increased the aconitase levels above those of the wild-type strain. These results demonstrate the direct regulation of the yggX gene by the redox-sensing SoxRS system and provide further evidence for the involvement of yggX in protection of iron-sulfur proteins against oxidative damage.

* Corresponding author. Mailing address: Department of Microbiology, University of Massachusetts, Morrill Science Center IV North, Amherst, MA 01003. Phone: (413) 577-4312. Fax: (413) 545-1578. E-mail: ppomposi{at}microbio.umass.edu.

Journal of Bacteriology, November 2003, p. 6624-6632, Vol. 185, No. 22
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.22.6624-6632.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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