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

Xenopus laevis oocytes respond to high temperature (>31°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 α-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.