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Journal of Bacteriology, April 1999, p. 2075-2083, Vol. 181, No. 7
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Disruption and Analysis of the clpB, clpC, and clpE Genes in Lactococcus lactis: ClpE, a New Clp Family in Gram-Positive Bacteria

Hanne Ingmer,1,* Finn K. Vogensen,1 Karin Hammer,2 and Mogens Kilstrup2

Centre for Advanced Food Studies, 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 23 September 1998/Accepted 12 January 1999

In the genome of the gram-positive bacterium Lactococcus lactis MG1363, we have identified three genes (clpC, clpE, and clpB) which encode Clp proteins containing two conserved ATP binding domains. The proteins encoded by two of the genes belong to the previously described ClpB and ClpC families. The clpE gene, however, encodes a member of a new Clp protein family that is characterized by a short N-terminal domain including a putative zinc binding domain (-CX2CX22CX2C-). Expression of the 83-kDa ClpE protein as well as of the two proteins encoded by clpB was strongly induced by heat shock and, while clpC mRNA synthesis was moderately induced by heat, we were unable to identify the ClpC protein. When we analyzed mutants with disruptions in clpB, clpC, or clpE, we found that although the genes are part of the L. lactis heat shock stimulon, the mutants responded like wild-type cells to heat and salt treatments. However, when exposed to puromycin, a tRNA analogue that results in the synthesis of truncated, randomly folded proteins, clpE mutant cells formed smaller colonies than wild-type cells and clpB and clpC mutant cells. Thus, our data suggest that ClpE, along with ClpP, which recently was shown to participate in the degradation of randomly folded proteins in L. lactis, could be necessary for degrading proteins generated by certain types of stress.

* Corresponding author. Present address: Institute of Veterinary Microbiology, The Royal Veterinary and Agricultural University, KVL, Stigbøjlen 4, DK-1870 Frederiksberg, Denmark. Phone: 45 3528 2706. Fax: 45 3528 2757. E-mail: ingmer{at}biobase.dk.

Journal of Bacteriology, April 1999, p. 2075-2083, Vol. 181, No. 7
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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