Abstract
We have studied modifications in the pattern of proteins synthesized by tobacco (Nicotiana tabacum var Maryland) mesophyll protoplasts when they are transferred from 25 degrees C to 40 degrees C. The synthesis of one group of proteins is practically unaffected by the heat shock. On the other hand, the synthesis of most other 25 degrees C proteins is greatly reduced, while specific heat-shock proteins appear: 17 stable, neutral, major proteins, which are synthesized throughout the culture period at the higher temperature and which correspond to those observed in other organisms, and two basic proteins with a short lifetime and which are synthesized only during the first 2 hours of heat shock. We suggest that these latter proteins are regulatory peptides which intervene in the inhibition of 25 degrees C syntheses.