HEAT SHOCK-INDUCED DNA RELAXATION IN-VITRO BY DNA GYRASE OF ESCHERICHIA-COLI IN THE PRESENCE OF ATP

Genetic studies revealed that DNA gyrase seems to catalyze immediate a nd transient DNA relaxation after Escherichia coli cells are exposed t o heat shock (Ogata, Y., Mizushima, T., Kataoka, K., Miki, T., and Sek imizu, K. (1994) Mol. Gen. Genet. 244, 451-455). We have now obtained biochemical evidence to support this hypothesis. DNA gyrase catalyzed an increase in the linking number of DNA and relaxation of negatively supercoiled DNA, under physiological concentrations of ATP. Analyses b y gel filtration chromatography of each subunit revealed that DNA rela xation activity co-migrated with each subunit. The linking number of D NA increased as the temperature increased. Further, the reaction was i nhibited by nalidixic acid or by oxolinic acid. Based on these results , we propose that DNA gyrase participates in a concerted reaction with DNA topoisomerases in the immediate relaxation of DNA in cells expose d to heat shock.