The heat shock response occurs in virtually all organisms, including bacteria. The response occurs when an environmental stress is imposed on the organism. The name of the response comes from its discovery following the application of a mild heat stress, only 5 to 10° C higher than the usual preferred growth temperature. However, the response, which can be more correctly thought of as an adaptive response, consisting of a temporary alteration in the metabolism of the organism, occurs in response to more than just excessive heat.

Hallmarks of the heat shock response are its rapid onset and short-term nature. The response is an emergency coping type of reaction to a conditions that is perceived by the organism as being threatening. The response is not a long-term commitment, such as the formation of a spore by a bacterium (although some proteins that are stimulated in the...