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Journal of Bacteriology, March 1999, p. 1537-1543, Vol. 181, No. 5
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Protein ProQ Influences Osmotic Activation of Compatible Solute Transporter ProP in Escherichia coli K-12

H. Jörg Kunte, Rebecca A. Crane, Doreen E. Culham, Deborah Richmond, and Janet M. Wood^*

Department of Microbiology, University of Guelph, Guelph, Ontario, Canada N1G 2W1

Received 9 September 1998/Accepted 9 December 1998

ProP is an osmoregulatory compatible solute transporter in Escherichia coli K-12. Mutation proQ220::Tn5 decreased the rate constant for and the extent of ProP activation by an osmotic upshift but did not alter proP transcription or the ProP protein level. Allele proQ220::Tn5 was isolated, and the proQ sequence was determined. Locus proQ is upstream from prc (tsp) at 41.2 centisomes on the genetic map. The proQ220::Tn5 and prc phenotypes were different, however. Gene proQ is predicted to encode a 232-amino-acid, basic, hydrophilic protein (molecular mass, 25,876 Da; calculated isoelectric point, 9.66; 32% D, E, R, or K; 54.5% polar amino acids). The insertion of PCR-amplified proQ into vector pBAD24 produced a plasmid containing the wild-type proQ open reading frame, the expression of which yielded a soluble protein with an apparent molecular mass of 30 kDa. Antibodies raised against the overexpressed ProQ protein detected cross-reactive material in proQ⁺ bacteria but not in proQ220::Tn5 bacteria. ProQ may be a structural element that influences the osmotic activation of ProP at a posttranslational level.

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^* Corresponding author. Mailing address: Department of Microbiology, University of Guelph, Guelph, ON N1G 2W1, Canada. Phone: (519) 824-4120, ext. 3866. Fax: (519) 837-1802. E-mail: jwood{at}uoguelph.ca.

Present address: Institut für Mikrobiologie und Biotechnologie, Universität Bonn, Bonn D53115, Germany.

Present address: 331 Breezewood Crescent, Waterloo, ON N2L 5K4, Canada.

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Journal of Bacteriology, March 1999, p. 1537-1543, Vol. 181, No. 5
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

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