Effect of Hyperthermia on Nonhistone Proteins Isolated with DNA

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Abstract
Hyperthermic treatment of CHO cells at 45.5°C resulted in an increase in nonhistone protein isolated with DNA. The increase, as measured by [3 H]tryptophan to [14 C]thymidine ratios, was proportional to heat duration and was 1.5 times the control after 15 min of heating. X irradiation (up to 3000 rad) had no effect on this result. If cells were incubated at 37°C after heating, recovery to control ratios occurred within 12 hr. Analysis of labeled protein by SDS slab gel electrophoresis showed that heat caused no consistent density or radioactivity differences in individual nonhistone bands. However, heat did produce a nonspecific overall increase in high molecular weight regions. These results were independent of the chromatin isolation technique (isotonic versus hypotonic) and of culturing conditions (monolayer versus suspension). Also, similar results were obtained when chromatin was isolated from either cells or nuclei. These results would support hypotheses for the mechanism of hyperthermic killing that invoke alteration of chromosomal proteins.