Identity elements in bovine tRNA^Trp required for the specific stimulation of gelonin, a plant ribosome-inactivating protein

Abstract

Ribosome-inactivating proteins (RIPs) are RNA-N-glycosidases widely present in plants that depurinate RNA in ribosomes at a specific universally conserved position, A4324, in the rat 28S rRNA. A small group of RIPs (cofactor-dependent RIPs) require ATP and tRNA to reach maximal activity on isolated ribosomes. Among cofactor-dependent RIPs, gelonin is specifically and uniquely stimulated by tRNA^Trp. The active species are avian (chicken) and mammalian (beef, rat, and rabbit) tRNA^Trp, whereas yeast tRNA^Trp is completely devoid of stimulating activity. In the present article, bovine and yeast tRNA^Trp with unmodified bases were prepared by assembly of the corresponding genes from synthetic oligonucleotides followed by PCR and T7 RNA polymerase transcription of the amplified products. The two synthetic tRNAs were fully active (bovine) or inactive (yeast) as the wild-type tRNAs. Construction of chimeric tRNA^Trp transcripts identified the following bovine nucleotides as recognition elements for gelonin-stimulating activity: G26 and bp G12-C23 in the D arm and G57, A59, and bp G51-C63 and U52-A62 in the T arm. Among single-stranded nucleotides, A59 has a prominent role, but full expression of the gelonin-stimulating activity requires an extensive cooperation between nucleotides in both arms.