"Prompt" heat shock proteins: translationally regulated synthesis of new proteins associated with the nuclear matrix-intermediate filaments as an early response to heat shock.

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Abstract
The response of mammalian cells, such as HeLa cells, to prolonged exposure to increased temperature (termed heat shock) was well characterized. New mRNA is synthesized for several proteins whose translation is best seen after a return to 37.degree. C. Another response to increased temperature of a distinctively different character is shown. A set of at least 50 newly detectable proteins, exclusively associated with the nuclear matrix-intermediate filament (NM-IF) fraction, is synthesized immediately upon exposure to high temperature. These are of very low abundance or nonexistent in the unstressed cell and none appear to correspond to the classic heat shock proteins produced after new transcription. Prior treatment with actinomycin D has little effect on these prompt proteins, and they appear to be made from preexisting mRNA that are activated at the increased temperature. The protein synthesis in the soluble, cytoskeletal and chromatin fractions is strongly reduced by the increased temperature, while the labeling of the prompt proteins associated with NM-IF complex rapidly rises severalfold above that in control cells. The 4 cell fractions are evidently not arbitrary cell divisions; rather they represent physiologically significant compartments in the cell.