The last two decades of the twentieth century saw the discovery of the heat-shock or cell-stress response, changes in the expression of certain proteins, and the unraveling of the function of proteins that mediate this essential cell-survival strategy. The proteins made in response to the stresses are called heat-shock proteins, stress proteins, or molecular chaperones. A large number of chaperones have been identified in bacteria (including archaebacteria), yeast, and eukaryotic cells. Fifteen different groups of proteins are now classified as chaperones. Their expression is often increased by cellular stress. Indeed, many were identified as heat-shock proteins, produced when cells were subjected to elevated temperatures. Chaperones likely function to stabilize proteins under less than ideal conditions.

The term chaperone was coined only in 1978, but the existence of chaperones is ancient, as evidenced by the conservation of the peptide sequences in the chaperones from prokaryotic and eukaryotic organisms, including humans...