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 g roEL homologues was carried out. Northern blot analysis showed a simil ar 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 an d grpE, resembled the pattern observed for the above genes, although m aximum induction was observed earlier for orf1 and grpE. Novel transcr ipt sizes were detected in heat-shocked cells. The induction kinetics observed for ftsH suggested a different regulation for this gene. Expe rimental evidence for a pronounced transcriptional regulation being in volved in the heat shock response in L, lactis MG1363 is presented. A gene located downstream of the dnaK operon in strain MG1363, named orf 4, was shown not to be regulated by heat shock.