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Journal of Bacteriology, August 2007, p. 5495-5503, Vol. 189, No. 15
0021-9193/07/$08.00+0     doi:10.1128/JB.00190-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

The Two-Component Regulatory System senX3-regX3 Regulates Phosphate-Dependent Gene Expression in Mycobacterium smegmatis{triangledown}

Robert T. Glover,1,2 Jordan Kriakov,1,2 Scott J. Garforth,2 Anthony D. Baughn,1,2 and William R. Jacobs Jr.1,2*

Howard Hughes Medical Institute,1 Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York 104612

Received 5 February 2007/ Accepted 15 May 2007

Phosphate import is required for the growth of mycobacteria and is regulated by environmental inorganic phosphate (Pi) concentrations, although the mechanism of this regulation has not been characterized. The expression of genes involved in Pi acquisition is frequently regulated by two-component regulatory systems (2CRs) consisting of a sensor histidine kinase and a DNA-binding response regulator. In this work, we have identified the senX3-regX3 2CR as a Pi-dependent regulator of genes involved in phosphate acquisition in Mycobacterium smegmatis. Characterization of senX3 mutants with different PhoA phenotypes suggests a dual role for SenX3 as a phosphatase or a phosphodonor for the response regulator RegX3, depending upon Pi availability. Expression of PhoA activity required phosphorylation of RegX3, consistent with a role for phosphorylated RegX3 (RegX3~P) as a transcriptional activator of phoA. Furthermore, purified RegX3~P bound to promoter sequences from phoA, senX3, and the high-affinity phosphate transporter component pstS, demonstrating direct transcriptional control of all three genes. DNase I footprinting and primer extension analyses have further defined the DNA-binding region and transcriptional start site within the phoA promoter. A DNA motif consisting of an inverted repeat was identified in each of the promoters bound by RegX3~P. Based upon our findings, we propose a model for Pi-regulated gene expression mediated by SenX3-RegX3 in mycobacteria.

* Corresponding author. Mailing address: Albert Einstein College of Medicine, Department of Microbiology and Immunology, 1300 Morris Park Avenue, Forchheimer 405, Bronx, NY 10461. Phone: (718) 430-2888. Fax: (718) 518-0366. E-mail: jacobs{at}aecom.yu.edu

{triangledown} Published ahead of print on 25 May 2007.

Journal of Bacteriology, August 2007, p. 5495-5503, Vol. 189, No. 15
0021-9193/07/$08.00+0     doi:10.1128/JB.00190-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



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