Abstract
Considerable attention has recently been focused on the role that denatured or otherwise “nonfunctional” proteins play in the induction of the heat shock response and the development of thermotolerance (Ananthan etal., 1986; Carlson etal., 1987; Hightower, 1980; Lee and Hahn, 1988; Magun and Fennie, 1981). The concept of denatured proteins is imprecise: in the context of heat shock, what is usually meant is that cytosolic proteins have parts or all of their hydrophobic regions uncovered. These normally well-hidden parts of the proteins then become reactive and, therefore, readily combine with other cellular components, thus preventing renaturation. To date, no technique has been reported that would permit quantifying the amount of denatured proteins within the cell either before, during, or after exposure to elevated temperatures. For this reason, the quantitative relationship between protein denaturation and induction of stress responses has not been investigated. We present data that suggest that this aspect of protein denaturation can readily be quantified, and we demonstrate that proteins that cannot be renatured, for whatever reason, may very likely be among the cellular lesions that are responsible for heat-induced cell death as well as being able to induce the heat shock response.