The mitochondria are recognition organelles of cell stress.

The cellular response to stress includes synthesis of specific stress proteins in the presence of a generalized suppression of protein synthesis. The response occurs in intact animals, individually stressed organs of intact animals, donor organs upon removal, regardless of preservation methods, and cells in culture. The molecular biology of stress protein induction is not understood. While stress proteins are beneficial, overall suppression of protein synthesis, if prolonged, is harmful. Since altered energy metabolism is integral to stress induction, we examined the mitochondria to determine if they could provide a possible molecular mechanism for initiating the response. Rat myoblasts were incubated at varying temperatures for up to 120 min in [35 S] methionine. Proteins were separated electrophoretically and newly synthesized proteins visualized autoradiographically. Isolated mitochondria from resting rat myoblasts were then stressed, label incorporation determined, and newly synthesized protein was visualized. Stress sharply suppressed protein synthesis in mitochondria but autoradiograms of stressed mitochondria showed that a single stress protein of 18 kDa was synthesized. Mitochondria independently respond to stress and synthesize a stress protein from their own DNA. This protein may provide an intermediary pathway that links stressful conditions in the environment to the overall response observed in the cell.