Heat-shock proteins, or stress proteins, are expressed in response to heat shock and a variety of other stress stimuli including oxidative free radicals and toxic metal ions. Sargent et al. (1989) identified a duplicated HSP70 locus in the class III region of the major histocompatibility complex on 6p21.3. A duplicated locus encoding the major heat shock-induced protein HSP70 is located in the major histocompatibility complex (MHC) class III region 92 kilobases (kb) telomeric to the C2 gene. The 70-kd mammalian heat shock proteins are structurally and functionally related to the uncoating protein that releases clathrin triskelia from coated vesicles.