[Construction of plasmids coding for diphtheria toxin fragments].

Plasmids coding different nontoxic derivatives (toxoids) of the diphtheria toxin were constructed. A secretion of toxoids that carry a signal sequence was found in the periplasmic space of E. coli and Erwinia carotovora. Toxoids without a signal sequence appear in the cytoplasm. We believe that the toxoids secreted in E. coli and E. carotovora cells undergo a limited proteolysis. According to the molecular weights of the fragments there are three targets for proteolysis. One of them being just between A- and B-fragments of the diphtheria toxin. The others are localised in the B-fragment. The role of E. coli signal peptidase in the specific cutting is discussed.