How the cell copes with stress and the function of heat shock proteins.

Virtually all cells, including the prokaryotic microorganisms and the highly differentiated eukaryotic cells in human tissues, contain a small set of normally silent genes that are rapidly activated by a heat shock that raises the temperature only 5 to 10% above that of the normal physiologic range for that organism. Concomitantly, many active genes are turned off. Other kinds of stress, such as exposure to alcohol or other organic agents, heavy metals, oxidants, and agents capable of perturbing protein structure, produce a similar response, and many of these activate the same set of genes. The proteins encoded by these stress-activated genes are called heat shock proteins (hsp). They are strongly conserved in structure among widely divergent biologic species, and many function as "molecular chaperones" by forming transient complexes with partially folded or misfolded polypeptides so as to prevent their irreversible denaturation. Most hsp are members of gene/protein families, and isoforms are frequently found under normal physiologic conditions in many compartments of the cell where they act also as chaperones, binding to a variety of polypeptides to facilitate folding, oligomerization, transport, metabolic activity, and degradation. Few of the polypeptide "targets" that complex with stress-induced forms of hsp have been identified, but a number of cellular components have been shown to be particularly stress sensitive.(ABSTRACT TRUNCATED AT 250 WORDS)