Cytotoxicity of a recombinant ricin‐A‐chain fusion protein containing a proteolytically‐cleavable spacer sequence

Chimeric proteins composed of ricin toxin A chain (RTA) and staphylococcal protein A (PA) have been produced in E. coli . Constructs consisting of N‐terminal RTA and C‐terminal PA (RTA‐PA) or N‐terminal PA and C‐terminal (PA‐RTA) were capable of binding to immunoglobulin G (via PA) and of specifically depurinating 28 S ribosomal RNA (via RTA). However, neither fusion protein was cytotoxic to antigen‐bearing target cells in the presence of an...