Abstract
soxR and soxS are adjacent genes that govern a superoxide response regulon. Previous studies revealed that induction of the regulon is accompanied by increased transcription of soxS, which can activate the target genes. Therefore, induction may occur in two stages: the soxR-dependent activation of soxS, followed by the soxS-dependent induction of other genes. However, the requirement for soxR was unproven because the only existing soxR mutations either were of the regulon-constitutive type or also involved soxS. Therefore, we produced an insertion mutation that was shown by complementation to inactivate only soxR. In confirmation of the two-stage model, soxR was required for the induction by paraquat of the target genes studied (nfo, zwf, and sodA), for paraquat resistance, and for the 47- to 76-fold induction of soxS-lacZ gene fusions. Paraquat did not affect the expression of soxR-lacZ gene fusions. In a soxRS deletion mutant, the regulon was constitutively activated by a runaway soxS+ plasmid. However, a lower-copy-number plasmid failed to activate nfo, zwf, or sodA but did increase the paraquat resistance of a soxRS mutant. Therefore, there is a differential response of the regulon genes to soxS overproduction. A soxR regulon-constitutive mutation was suppressed by a soxR+ plasmid, suggesting a competition between native and activated forms of SoxR. It is proposed that to enhance the sensitivity of the response, the cell minimizes such potential competition by manufacturing only a small amount of this sensor protein, thereby necessitating signal amplification via induction of soxS.
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Selected References
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- Amábile-Cuevas C. F., Demple B. Molecular characterization of the soxRS genes of Escherichia coli: two genes control a superoxide stress regulon. Nucleic Acids Res. 1991 Aug 25;19(16):4479–4484. doi: 10.1093/nar/19.16.4479. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Beck C. F., Warren R. A. Divergent promoters, a common form of gene organization. Microbiol Rev. 1988 Sep;52(3):318–326. doi: 10.1128/mr.52.3.318-326.1988. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Bittner M., Vapnek D. Versatile cloning vectors derived from the runaway-replication plasmid pKN402. Gene. 1981 Dec;15(4):319–329. doi: 10.1016/0378-1119(81)90175-x. [DOI] [PubMed] [Google Scholar]
- Chan E., Weiss B. Endonuclease IV of Escherichia coli is induced by paraquat. Proc Natl Acad Sci U S A. 1987 May;84(10):3189–3193. doi: 10.1073/pnas.84.10.3189. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Chung C. T., Niemela S. L., Miller R. H. One-step preparation of competent Escherichia coli: transformation and storage of bacterial cells in the same solution. Proc Natl Acad Sci U S A. 1989 Apr;86(7):2172–2175. doi: 10.1073/pnas.86.7.2172. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Cunningham R. P., Saporito S. M., Spitzer S. G., Weiss B. Endonuclease IV (nfo) mutant of Escherichia coli. J Bacteriol. 1986 Dec;168(3):1120–1127. doi: 10.1128/jb.168.3.1120-1127.1986. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Demple B., Amábile-Cuevas C. F. Redox redux: the control of oxidative stress responses. Cell. 1991 Nov 29;67(5):837–839. doi: 10.1016/0092-8674(91)90355-3. [DOI] [PubMed] [Google Scholar]
- Greenberg J. T., Monach P., Chou J. H., Josephy P. D., Demple B. Positive control of a global antioxidant defense regulon activated by superoxide-generating agents in Escherichia coli. Proc Natl Acad Sci U S A. 1990 Aug;87(16):6181–6185. doi: 10.1073/pnas.87.16.6181. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Kao S. M., Hassan H. M. Biochemical characterization of a paraquat-tolerant mutant of Escherichia coli. J Biol Chem. 1985 Sep 5;260(19):10478–10481. [PubMed] [Google Scholar]
- Ronson C. W., Nixon B. T., Ausubel F. M. Conserved domains in bacterial regulatory proteins that respond to environmental stimuli. Cell. 1987 Jun 5;49(5):579–581. doi: 10.1016/0092-8674(87)90530-7. [DOI] [PubMed] [Google Scholar]
- Simons R. W., Houman F., Kleckner N. Improved single and multicopy lac-based cloning vectors for protein and operon fusions. Gene. 1987;53(1):85–96. doi: 10.1016/0378-1119(87)90095-3. [DOI] [PubMed] [Google Scholar]
- Smith P. K., Krohn R. I., Hermanson G. T., Mallia A. K., Gartner F. H., Provenzano M. D., Fujimoto E. K., Goeke N. M., Olson B. J., Klenk D. C. Measurement of protein using bicinchoninic acid. Anal Biochem. 1985 Oct;150(1):76–85. doi: 10.1016/0003-2697(85)90442-7. [DOI] [PubMed] [Google Scholar]
- Sutcliffe J. G. Complete nucleotide sequence of the Escherichia coli plasmid pBR322. Cold Spring Harb Symp Quant Biol. 1979;43(Pt 1):77–90. doi: 10.1101/sqb.1979.043.01.013. [DOI] [PubMed] [Google Scholar]
- Tsaneva I. R., Weiss B. soxR, a locus governing a superoxide response regulon in Escherichia coli K-12. J Bacteriol. 1990 Aug;172(8):4197–4205. doi: 10.1128/jb.172.8.4197-4205.1990. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Winans S. C., Elledge S. J., Krueger J. H., Walker G. C. Site-directed insertion and deletion mutagenesis with cloned fragments in Escherichia coli. J Bacteriol. 1985 Mar;161(3):1219–1221. doi: 10.1128/jb.161.3.1219-1221.1985. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Wu J., Weiss B. Two divergently transcribed genes, soxR and soxS, control a superoxide response regulon of Escherichia coli. J Bacteriol. 1991 May;173(9):2864–2871. doi: 10.1128/jb.173.9.2864-2871.1991. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Yanisch-Perron C., Vieira J., Messing J. Improved M13 phage cloning vectors and host strains: nucleotide sequences of the M13mp18 and pUC19 vectors. Gene. 1985;33(1):103–119. doi: 10.1016/0378-1119(85)90120-9. [DOI] [PubMed] [Google Scholar]