INDUCED LEVELS OF HEAT-SHOCK PROTEINS IN A DNAK MUTANT OF LACTOCOCCUS-LACTIS

The bacterial heat shock response is characterized by the elevated exp ression of a number of chaperone complexes and proteases, including th e DnaK-GrpE-DnaJ and the GroELS chaperone complexes. In order to inves tigate the importance of the DnaK chaperone complex for growth and hea t shock response regulation in Lactococcus lactis, we have constructed two dnaK mutants with C-terminal deletions in dnaK. The minor deletio n of 65 amino acids in the dnaK Delta 2 mutant resulted in a slight te mperature-sensitive phenotype. BK6, containing the larger deletion of 174 amino acids (dnaK Delta 1), removing the major part of the inferre d substrate binding site of the DnaK protein, exhibited a pronounced t emperature-sensitive phenotype and showed altered regulation of the he at shock response. The expression of the heat shock proteins was incre ased at the normal growth temperature, measured as both protein synthe sis rates and mRNA levels, indicating that DnaK could be involved in t he regulation of the heat shock response in L. lactis. For Bacillus su btilis, it has been found (A. Mogk, G. Homuth, C. Scholz, L. Kim, F. X . Schmid, and W. Schumann, EMBO J. 16:4579-3590, 1997) that the activi ty of the heat shock repressor HrcA is dependent on the chaperone func tion of the GroELS complex and that a dnaK insertion mutant has no eff ect on the expression of the heat shock proteins. The present data fro m L. lactis suggest that the DnaK protein could be involved in the mat uration of the homologous HrcA protein in this bacterium.