RELAXATION OF SUPERCOILED DNA ASSOCIATED WITH INDUCTION OF HEAT-SHOCKPROTEINS IN ESCHERICHIA-COLI

Heat treatment of wild-type Escherichia coli cells led to a transient relaxation of negatively supercoiled plasmid DNA and there was no reco very of DNA torsional strain in the DNA in gyrA mutant cells. After he at treatment, DnaK and GroEL proteins were synthesized continuously in the gyrA mutant cells, whereas they were synthesized only transiently in wild-type cells. Thus, change in superhelical density of the DNA c orrelated with the temperature-induced expression of heat shock protei ns. Inhibitors of DNA gyrase (nalidixic acid, novobiocin), an organic solvent (ethanol) and a psychotropic drug (chlorpromazine) all stimula ted relaxation of cellular DNA over the same concentration range that induces heat shock proteins. As DNA relaxation was induced by heat tre atment or chemicals in an rpoH mutant, the process is not the result o f induced synthesis of heat shock proteins.