Heat-shock proteins, molecular chaperones, and the stress response: Evolutionary and ecological physiology

Molecular chaperones, including the heat-shock proteins (Hsps), are a ubiqu itous feature of cells in which these proteins cope with stress-induced den aturation of other proteins, Hsps have received the most attention in model organisms undergoing experimental stress in the laboratory, and the functi on of Hsps at the molecular and cellular level is becoming well understood in this context. A complementary focus is now emerging on the Hsps of both model and nonmodel organisms undergoing stress in nature, on the roles of H sps in the stress physiology of whole multicellular eukaryotes and the tiss ues and organs they comprise, and on the ecological and evolutionary correl ates of variation in Hsps and the genes that encode them. This focus disclo ses that (a) expression of Hsps can occur in nature, (b) all species have h sp genes but they vary in the patterns of their expression, (c) Hsp express ion can be correlated with resistance to stress, and (d) species' threshold s for Hsp expression are correlated with levels of stress that they natural ly undergo. These conclusions are now well established and may require litt le additional confirmation; many significant questions remain unanswered co ncerning both the mechanisms of Hsp-mediated stress tolerance at the organi smal level and the evolutionary mechanisms that have diversified the hsp ge nes.