Characterization of a 42°C-Specific Heat Shock Protein of Mammalian Cells1

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Abstract
HeLa cells synthesize a particular heat shock protein that is induced only by heat shock at 42°C, and not at 45°C or by other stresses that induce major heat shock proteins (Hatayama et al. (1986) Biochem. Biophys. Res. Commun. 137, 957–963). We further characterized the 42°C-specific protein. This protein was induced in mouse FM 3A cells as well as in human HeLa cells. In both cell lines, the protein was resolved into two spots, a basic polypeptide and an acidc one. The mRNA of the protein was induced during the incubation of these cells at 42°C, and the in vitro translation product of mRNA corresponded to the basic, not to the acidic, polypeptide. During the chase period for cells that were labeled with [35S]-methionine, the basic polypeptide of the protein decreased, and the acidic one increased, indicating that the protein was synthesized as the basic polypeptide and then somehow modified to become the acidic one. The 42°C-specific protein was found only in the cytosol fraction, and not in the nuclear or other particulate fractions, in both HeLa and FM 3A cells. The results suggested that the 42°C-specific protein may have some function in the cytoplasm of mammalian cells during mild heat shock.