STRESS-INDUCED TRANSCRIPTIONAL ACTIVATION

Living cells, both prokaryotic and eukaryotic, employ specific sensory and signalling systems to obtain and transmit information from their environment in order to adjust cellular metabolism, growth, and develo pment to environmental alterations Among external factors that trigger such molecular communications are nutrients, ions drugs and other com pounds, and physical parameters such as temperature and pressure. One could consider stress imposed on cells as any disturbance of the norma l growth condition and even as any deviation from optimal growth circu mstances. It may be worthwhile to distinguish specific and general str ess circumstances. Reasoning from this angle, the extensively studied response to heat stress on the one hand is a specific response of cell s challenged with supra-optimal temperatures. This response makes use of the sophisticated chaperoning mechanisms playing a role during norm al protein folding and turnover. The response is aimed primarily at pr otection and repair of cellular components and partly at acquisition o f heat tolerance. In addition heat stress conditions induce a general response, in common with other metabolically adverse circumstances lea ding to physiological perturbations such as oxidative stress or osmost ress. Furthermore, it is obvious that limitation of essential nutrient s, such as glucose or amino acids for yeasts, leads to such a metaboli c response. The purpose of the general response may be to promote rapi d recovery from the stressful condition and resumption of normal growt h. This review focuses on the changes in gene expression that occur wh en cells are challenged by stress, with major emphasis on the transcri ption factors involved, their cognate promoter elements and the modula tion of their activity upon stress signal transduction. With respect t o heat shock-induced changes, a wealth of information on both prokaryo tic and eukaryotic organisms including yeasts, is available. As far as the concept of the general (metabolic) stress response is concerned m ajor attention will be paid to Saccharomyces cerevisiae.