Direct molecular cloning and expression of two distinct abrin A-chains

The protein toxin abrin, which possesses an N-glycosylase activity toward eukaryotic 28 S rRNA, may have a potential in the deliberate eradication of certain cells. Here we report, by polymerase chain reaction technique, the isolation of genomic DNA sequences encoding two distinct abrin A-chains. A third sequence which encoded a part of a third type of A-chain was also isolated. The deduced amino acid sequences of the two full-length A-chains were about 84% similar. Addition of mRNA encoding the full-length A-chains to reticulocyte lysate strongly inhibited protein synthesis in the lysates, and a corresponding glycosylase activity on rRNA was observed. Addition of the same mRNA to toxin-resistant wheat germ extracts led to synthesis of the expected 30-kDa protein which could be precipitated with antibodies specific for abrin.