THE MAJOR ELDERBERRY (SAMBUCUS-NIGRA) FRUIT PROTEIN IS A LECTIN DERIVED FROM A TRUNCATED TYPE-2 RIBOSOME-INACTIVATING PROTEIN

The major protein of elderberry (Sambucus nigra L.) fruits is a lectin , called Sambucus nigra agglutinin IVf or SNAIVf. This lectin is compo sed of subunits that strongly resemble the B chain of the type 2 ribos ome-inactivating protein (RIP), called SNAVf, present in the same tiss ue. To corroborate the possible relationship between both proteins the ir corresponding cDNAs were cloned and compared. Alignment of the dedu ced amino acid sequences revealed that the cDNA encoding SNAIVf is alm ost identical to that of SNAVf except that its A chain is truncated. N orthern blot analysis confirmed that the mRNA encoding SNAIVf is about 500 nucleotides shorter than the SNAVf mRNA. In addition, the occurre nce of a truncated type 2 RIP gene was unambiguously demonstrated by t he analysis of PCR amplified genomic sequences. These results not only demonstrate for the first time that a plant lectin is encoded by a tr uncated type 2 RIP gene but also address important questions with resp ect to the molecular evolution of RIP and lectins.