The heat-shock response in Xenopus oocytes is controlled at the translational level.

Xenopus laevis oocytes respond to high temperature (greater than 31 degrees C) by the synthesis of one major (70 kilodalton) protein and by a gradual reduction in the rate of normal protein synthesis. In contrast with most other cells, the heat-shock response of Xenopus oocytes is controlled exclusively at the translational level. Enucleated or alpha-amanitin-injected oocytes synthesize normal levels of heat-shock protein. Thus high temperature induces the translation of preformed heat-shock mRNA. This continues for more than a day after a shift back to a normal temperature, but ceases within 2 days. Heat-shock protein synthesis can be sequentially induced and inactivated in the same oocyte over several days. We conclude that an oocyte contains 10-100 pg of heat-shock mRNA, which is synthesized during oogenesis at the normal temperature, and which is stored in an inactive state by a "masking" mechanism.