Résumé
Ricin is a type II ribosome-inactivating protein which occurs in the seeds of the castor oil plant. Cloning is almost invariably followed by attempts to express and subsequently manipulate the encoding DNA. In the cloning of other toxin genes with agglutinin counterparts, it will likewise be important to distinguish the two types of sequences. In vitro manipulation of RTB sequences generated full-length clones as convenient cassettes suitable for subcloning and expression purposes. Ricin E cDNA clones have been obtained using a method involving homopolymer tailing of SS cDNAs and subsequent priming of second-strand synthesis with a complementary homopolymer. A ricin genomic clone with a coding sequence apparently differing in only base position from that above has been described. The significance of this relates to the use of the ricin leader sequence in heterologous expression systems where it is important to define the protein product made. A variety of strategies have been used to obtain cDNA and genomic clones encoding ricin.