TYPE-1 RIBOSOME-INACTIVATING PROTEINS ARE THE MOST ABUNDANT PROTEINS IN IRIS (IRIS-HOLLANDICA VAR PROFESSOR BLAAUW) BULBS - CHARACTERIZATION AND MOLECULAR-CLONING

The most abundant protein of Iris bulbs has been identified as a type 1 ribosome-inactivating protein (RIP). Analysis of the purified protei ns and molecular cloning of the corresponding cDNAs demonstrated that this type 1 RIP is a mixture of three isoforms that exhibit a high deg ree of sequence identity and have similar, though not identical, ribos ome-inactivating and polynucleotide :adenosine glycosidase activities. The accumulation of large quantities of type 1 RIP in a vegetative st orage organ suggests that this presumed defence-related protein also p lays a role in the nitrogen-storage metabolism of the bulb.