Analysis of heat shock gene expression in Lactococcus lactis MG1363.

The induction of the heat shock response in Lactococcus lactis subsp. cremoris strain MG1363 was analysed at the RNA level using a novel RNA isolation procedure to prevent degradation. Cloning of the dnaJ and groEL homologues was carried out. Northern blot analysis showed a similar induction pattern for dnaK, dnaJ and groELS after transfer from 30 degrees C to 43 degrees C when MG1363 was grown in defined medium. The dnaK gene showed a 100-fold induction level 15 min after temperature shifting. Induction of the first two genes in the dnaK operon, orf1 and grpE, resembled the pattern observed for the above genes, although maximum induction was observed earlier for orf1 and grpE. Novel transcript sizes were detected in heat-shocked cells. The induction kinetics observed for ftsH suggested a different regulation for this gene. Experimental evidence for a pronounced transcriptional regulation being involved in the heat shock response in L. lactis MG1363 is presented. A gene located downstream of the dnaK operon in strain MG1363, named orf4, was shown not to be regulated by heat shock.