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Abstract
A family of toxic proteins, the isoabrins, which possess N-glycosylase activity toward eukaryotic 28S rRNA, may have potential use in cancer chemotherapy. By polymerase chain reaction techniques, cDNA clones of three isoabrins, carrying A and B-chain sequences, were isolated and their nucleotide sequences were determined. The isoabrins consist of an A-chain comprised of 250 or 251 amino acids, followed by a 10 amino acid linker and a B-chain of 267 amino acids. There is substantial conservation in the B-chain of the three isoabrins, with less than six amino acid substitutions, whereas as many as 46 amino acid substitutions occur in the A-chains.