A cya deletion mutant of Escherichia coli develops thermotolerance but does not exhibit a heat-shock response.

An adenyl cyclase deletion mutant (cya) of E. coli failed to exhibit a heat-shock response even after 30 min at 42 degrees C. Under these conditions, heat-shock protein synthesis was induced by 10 min in the wild-type strain. These results suggest that synthesis of heat-shock proteins in E. coli requires the cya gene. This hypothesis is supported by the finding that a presumptive cyclic AMP receptor protein (CRP) binding site exists within the promoter region of the E. coli htpR gene. In spite of the absence of heat-shock protein synthesis, when treated at 50 degrees C, the cya mutant is relatively more heat resistant than wild type. Furthermore, when heat shocked at 42 degrees C prior to exposure at 50 degrees C, the cya mutant developed thermotolerance. These results suggest that heat-shock protein synthesis is not essential for development of thermotolerance in E. coli.