ABSTRACT
The widespread occurrence of single-chain ribosome-inactivating proteins (RIP) throughout the plant kingdom is an established fact. Several type I RIPs were isolated from Saponaria officinalis. However, whether these differences are due to selective action on ribosomes and not to some form of differential susceptibility of the various RIPs to the experimental conditions employed by the authors remains to be ascertained. Most of the toxin cloning studies have revealed multiple related toxin genes in plants. To date, very few studies have been reported on the genomic organization and sequence of type I RIPs and their transcripts. Two clones were selected for further analysis and were characterized by subcloning into EcoRl- digested M13 mp8 in both directions of insertion. The biosynthesis of ricin has been investigated in considerable detail, showing a close relationship between its biosynthetic pathway and that of several storage proteins and lectins accumulating in the seeds of Ricinus communis and of other plants.
