Macromolecule synthesis in HeLa cells after thermal shock.

The incorporation of radioactivity into HeLa cell polypeptides and DNA after exposure to 45 degrees C heating for 15 min was measured by continuous exposure to radiolabeled precursors. Both polypeptide and DNA synthesis were inhibited by thermal shock. The rate of incorporation of radiolabeled amino acids into whole cell, nuclear, or histone protein recovered to control levels by 5 to 8 hr after thermal shock. The rate of incorporation of radiolabeled thymidine into DNA did not recover to a control level within the first 8 hr after thermal shock. Thermal effects on amino acid and nucleotide precursor pools could not explain the inhibition of either protein or DNA synthesis. Since histone protein synthesis recovers prior to DNA synthesis, we conclude that the inhibition of histone protein synthesis after thermal shock is not responsible for the depression in synthesis of cellular DNA.