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Journal of Bacteriology, October 2003, p. 6042-6050, Vol. 185, No. 20
0021-9193/03/$08.00+0 DOI: 10.1128/JB.185.20.6042-6050.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Gert Dandanell,1 Anne-Marie Gilles,2 Octavian Barzu,2 Rod A. Kelln,3 and Jan Neuhard1*
Department of Biological Chemistry, Institute of Molecular Biology, University of Copenhagen, DK-1307 Copenhagen K, Denmark,1 Laboratoire de Chimie Structurale de Macromolécules, Institut Pasteur, 75724 Paris Cedex 15, France,2 Department of Chemistry and Biochemistry, University of Regina, Regina, Saskatchewan, Canada, S4S 0A23
Received 20 March 2003/ Accepted 16 July 2003
Salmonella enterica, in contrast to Escherichia coli K12, can use 2-deoxy-D-ribose as the sole carbon source. The genetic determinants for this capacity in S. enterica serovar Typhimurium include four genes, of which three, deoK, deoP, and deoX, constitute an operon. The fourth, deoQ, is transcribed in the opposite direction. The deoK gene encodes deoxyribokinase. In silico analyses indicated that deoP encodes a permease and deoQ encodes a regulatory protein of the deoR family. The deoX gene product showed no match to known proteins in the databases. Deletion analyses showed that both a functional deoP gene and a functional deoX gene were required for optimal utilization of deoxyribose. Using gene fusion technology, we observed that deoQ and the deoKPX operon were transcribed from divergent promoters located in the 324-bp intercistronic region between deoQ and deoK. The deoKPX promoter was 10-fold stronger than the deoQ promoter, and expression was negatively regulated by DeoQ as well as by DeoR, the repressor of the deoxynucleoside catabolism operon. Transcription of deoKPX but not of deoQ was regulated by catabolite repression. Primer extension analysis identified the transcriptional start points of both promoters and showed that induction by deoxyribose occurred at the level of transcription initiation. Gel retardation experiments with purified DeoQ illustrated that it binds independently to tandem operator sites within the deoQ and deoK promoter regions with Kd values of 54 and 2.4 nM, respectively.
Present address: Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA 50011.
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