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Journal of Bacteriology, August 1998, p. 3873-3881, Vol. 180, No. 15
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Induced Levels of Heat Shock Proteins in a dnaK Mutant of Lactococcus lactis

Birgit Koch,1 Mogens Kilstrup,2 Finn K. Vogensen,1 and Karin Hammer2,*

Department of Dairy and Food Science, The Royal Veterinary and Agricultural University, DK-1958 Frederiksberg C,1 and Department of Microbiology, Technical University of Denmark, DK-2800 Lyngby,2 Denmark

Received 24 November 1997/Accepted 28 May 1998

The bacterial heat shock response is characterized by the elevated expression of a number of chaperone complexes and proteases, including the DnaK-GrpE-DnaJ and the GroELS chaperone complexes. In order to investigate the importance of the DnaK chaperone complex for growth and heat shock response regulation in Lactococcus lactis, we have constructed two dnaK mutants with C-terminal deletions in dnaK. The minor deletion of 65 amino acids in the dnaKDelta 2 mutant resulted in a slight temperature-sensitive phenotype. BK6, containing the larger deletion of 174 amino acids (dnaKDelta 1), removing the major part of the inferred substrate binding site of the DnaK protein, exhibited a pronounced temperature-sensitive phenotype and showed altered regulation of the heat shock response. The expression of the heat shock proteins was increased at the normal growth temperature, measured as both protein synthesis rates and mRNA levels, indicating that DnaK could be involved in the regulation of the heat shock response in L. lactis. For Bacillus subtilis, it has been found (A. Mogk, G. Homuth, C. Scholz, L. Kim, F. X. Schmid, and W. Schumann, EMBO J. 16:4579-4590, 1997) that the activity of the heat shock repressor HrcA is dependent on the chaperone function of the GroELS complex and that a dnaK insertion mutant has no effect on the expression of the heat shock proteins. The present data from L. lactis suggest that the DnaK protein could be involved in the maturation of the homologous HrcA protein in this bacterium.

* Corresponding author. Mailing address: Department of Microbiology, Technical University of Denmark, DK-2800 Lyngby, Denmark. Phone: 45 45 25 24 96. Fax: 45 45 88 26 60. E-mail: kh{at}im.dtu.dk.

Journal of Bacteriology, August 1998, p. 3873-3881, Vol. 180, No. 15
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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