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Journal of Bacteriology, December 2003, p. 6756-6763, Vol. 185, No. 23
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.23.6756-6763.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

The pqrAB Operon Is Responsible for Paraquat Resistance in Streptomyces coelicolor

You-Hee Cho,1 Eun-Ja Kim,2,3 Hye-Jung Chung,2,{dagger} Jae-Hyun Choi,2 Keith F. Chater,3 Bo-Eun Ahn,2 Jung-Ho Shin,2 and Jung-Hye Roe2*

Department of Life Science, Sogang University, Seoul 121-742,1 School of Biological Sciences and Institute of Microbiology, Seoul National University, Seoul 151-742, Korea,2 Department of Molecular Microbiology, John Innes Centre, Norwich NR4 7UH, United Kingdom3

Received 13 January 2003/ Accepted 8 September 2003

Paraquat (methyl viologen)-resistant mutants of Streptomyces coelicolor A3(2) that grew and sporulated normally in the presence of paraquat were isolated. Based on the positions of the mutant loci in the genetic map, we isolated the pqr (paraquat resistance) gene whose mutation (pqr501) caused a dominant paraquat-resistant phenotype. The pqr locus consists of two genes (pqrA and pqrB) that form a transcription unit. The pqrA gene encodes a protein with a TetR-like DNA-binding motif, and the pqrB gene encodes a putative efflux pump of the major facilitator superfamily. The pqr501 mutation was a base substitution changing arginine-18 to glutamine (R18Q) near the helix-turn-helix motif in PqrA. A pqrA null mutant exhibited similar paraquat resistance, and an increase in the amount of pqrA promoter-driven transcripts of about eightfold was observed for the pqrA501 mutant. These results suggest that PqrA is a negative regulator of its own operon. Deletion of the pqrAB operon caused cells to be very sensitive to paraquat, consistent with the prediction that PqrB may function as a paraquat-efflux pump. Purified PqrA protein specifically bound to the pqrA promoter region, whereas mutant R18Q protein did not, indicating that PqrA is a direct autoregulator of its own operon.

* Corresponding author. Mailing address: School of Biological Sciences and Institute of Microbiology, Seoul National University, Seoul 151-742, Korea. Phone: 82-2-880-6706. Fax: 82-2-888-4911. E-mail: jhroe{at}plaza.snu.ac.kr.

{dagger} Present address: Laboratory of Pathology, DCS, NCI, National Institutes of Health, Bethesda, Md.

Journal of Bacteriology, December 2003, p. 6756-6763, Vol. 185, No. 23
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.23.6756-6763.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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