Occurrence and Taxonomical Distribution of Ribosome‐inactivating Proteins Belonging to the Ricin/Shiga Toxin Superfamily

Screening of the available plant genomes and transcriptomes revealed that ribosome-inactivating proteins (RIPs) are far more widespread that what can be inferred from protein studies. The existing lists of RIPs have to be extended both horizontally and vertically because RIP genes could be retrieved in numerous ‘novel’ species and genome analyses revealed the occurrence of complex RIP gene families in some plant species. Screening of prokaryotic genomes demonstrated that the occurrence of the RIP domain extends well beyond the classical Shiga toxin family. Moreover, it appears that besides in plants and bacteria genes with a RIP domain also occur in fungi and insects. Concomitant with the identification of numerous novel RIP genes the screening of the genome/transcriptome databases resulted in the identification of several novel domain architectures, which extends the present list of chimeric RIP genes and urges to readdress the issue of the molecular evolution of the RIP gene family.