3'-IMMATURE TRNA(TRP) IS REQUIRED FOR RIBOSOME INACTIVATION BY GELONIN, A PLANT RNA N-GLYCOSIDASE

Inactivation of ribosomes by gelonin, a ribosome-inactivating protein with RNA N-glycosidase activity on 28S rRNA, requires macromolecular c ofactors present in post-ribosomal supernatants. One of these cofactor s has been purified from a rat liver extract and identified as an RNA about 70 nt long which in sequence analysis shows a high level of simi larity with mammalian (bovine) tRNA(Trp). Th, pattern of the sequencin g gel is consistent with the co-existence in the preparation of two 3' -immature tRN(Trp) species, missing only A75, or both A75 and C74. In the presence of ATP, CTP and tRNA nucleotidyltransferase, the gelonin- stimulating RNA is a good acceptor of tryptophan. An oligodeoxynucleot ide complementary to positions 55 to 72 of mammalian (bovine) tRNA(Trp ) hybridizes with the gelonin-stimulating RNA as demonstrated by gel m obility shift and ribonuclease H digestion. The oligodeoxynucleotide-d irected ribonuclease H treatment also abolishes the gelonin-promoting activity of crude preparations of RNA, giving strong evidence that the only active RNA is a tRNA(Trp)-like molecule.