The Synechocystis model of stress:: From molecular chaperones to membranes

A highly conserved and exquisitely regulated cellular response to most stress conditions, such as cold, heat and visible or UV-light, is common to all organisms. Cells that have been pre-exposed to a sublethal dose of these stimuli can acquire a transient resistance against the killing effect of a subsequent stress. Specific membrane lipids and stress proteins, many of them molecular chaperones, play a fundamental role in these acclimation processes. According to the presently discussed model, cellular membranes are not simply the primary sites of stress damage, they are also able to sense extreme environmental changes and to activate stress-defence genes remotely as a consequence of a rapid modification in their physical state and microdomain organisation. Underlying the interdependence of the redox sensory pathway and membrane fluidity, sudden changes in membrane order can be signaled to gene expression via the light requiring redox sensory pathway. The photosynthetic Synecho-cystis PCC 6803 has several features that render it a particularly suitable model for such studies. While the general assembly and lipid composition of its thylakoid is similar to that of higher plants, it can easily be transformed by foreign DNA. Nonetheless, its whole genome has been determined and has become available via the internet. (C) Elsevier, Paris.