DIFFERENTIAL UP-REGULATION BY TRANSFER-RNAS OF RIBOSOME-INACTIVATING PROTEINS

Some plant ribosome-inactivating proteins (RIPs) with RNA-N-glycosidas e activity on 28S RNA require, for the inactivation of ribosomes, the presence of macromolecular cofactors present in post-ribosomal superna tants. In the case of gelonin one of the cofactors is tRNA(Trp) lackin g one or two nucleotides at the 3'-CCA end [Brigotti, M., Carnicelli, D., Alvergna, P., Pallanca, A., Lorenzetti, R., Denaro, M., Sperti, S. and Montanaro, L. (1995) Biochem. J. 310, 249-253]. In the present st udy it is shown that tRNAs are involved in the up-regulation of all th e cofactor-requiring RIPs up to now identified (agrostin, barley RIP, PAP and tritin, besides gelonin). Polyacrylamide gel electrophoresis s hows that tRNA fractions with different mobilities stimulate different RIPs. With the identification of agrostin, the cofactor-requiring RIP s (italics) add to five out of a total of thirteen investigated: barle y RIP, bryodin-R, gelonin, lychnin, momordin, momorcochin-S, PAP, sapo rin-6, tritin [Carnicelli, D., Brigotti, M., Montanaro, L. and Sperti, S. (1992) Biochem. Biophys. Res. Commun. 182, 579-582], agrostin, luf fin, trichokirin and trichosanthin (present study).