CONSTRUCTION AND EXPRESSION IN ESCHERICHIA-COLI OF HYBRID GENES COMPOSED OF SEQUENCES ENCODING DIPHTHERIA-TOXIN AND HUMAN CD4 RECEPTOR

Derivatives of natural toxins possessing substituted receptor-recognit ion domains of different specificities can be used as instruments for the selective elimination of target cells. We have constructed two dif ferent types of hybrid genes that encode proteins composed of diphther ia toxin (DT) lacking the C-terminal residues that mediate toxin bindi ng fused with the N-terminal region of human CD4 (Lys(10) to GlU(152)) . One of these hybrids encodes a protein with CD4 at the N terminus, w hile the other encodes a protein with CD4 at the C terminus. The stabi lity of these two proteins was dramatically different. We could not de tect a full-size product when the first construct was expressed in Esc herichia coli. In contrast, proteins encoded by the second construct w ere more stable. In the latter case, the amount of full-size hybrid pr otein was 1-2% of the total cell protein. We speculate on the involvem ent of the region that resembles the processing site of Pseudomonas ae ruginosa exotoxin A in the proteolytic degradation of the product enco ded by the first type of hybrid.