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Journal of Bacteriology, December 1998, p. 6743-6748, Vol. 180, No. 24
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Superimposition of TyrR Protein-Mediated Regulation on Osmoresponsive Transcription of Escherichia coli proU In Vivo

J. Gowrishankar1,* and A. J. Pittard2

Centre for Cellular & Molecular Biology, Hyderabad 500007, India,1 and Department of Microbiology and Immunology, University of Melbourne, Parkville, Victoria 3052, Australia2

Received 15 June 1998/Accepted 5 October 1998

Osmotic regulation of proU expression in the enterobacteria is achieved, at least in part, by a repression mechanism involving the histone-like nucleoid protein H-NS. By the creation of binding sites for the TyrR regulator protein in the vicinity of the sigma 70-controlled promoter of proU in Escherichia coli, we were able to demonstrate a superposed TyrR-mediated activation by L-phenylalanine (Phe), as well as repression by L-tyrosine, of proU expression in vivo. Based on the facts that pronounced activation in the presence of Phe was observed even at a low osmolarity and that the affinity of binding of TyrR to its cognate sites on DNA is not affected by Phe, we argue that H-NS-mediated repression of proU at a low osmolarity may not involve a classical silencing mechanism. Our data also suggest the involvement of recruited RNA polymerase in the mechanism of antirepression in E. coli.

* Corresponding author. Mailing address: Centre for Cellular & Molecular Biology, Uppal Rd., Hyderabad 500007, India. Phone: 91-40-7172241. Fax: 91-40-7171195. E-mail: shankar{at}ccmb.ap.nic.in.

Journal of Bacteriology, December 1998, p. 6743-6748, Vol. 180, No. 24
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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