Synthesis and function of isopentenyl adenosine derivatives in tRNA

Cytokinins - recent news and views of evolutionally old molecules

“…Certain tRNAs that bind to codons starting with an uracil contain, at position 37, an adenine residue modified by an isopentenyl moiety (Golovko et al 2000). Such prenylation of tRNA belongs to nucleotide hypermodifications that are important for the efficiency and fidelity of protein translation by the ribosome (reviewed by Persson et al 1994). The enzyme involved in the adjustment is tRNA-specific isopentenyltransferase (tRNA-IPT).…”

“…From the evolutionally fixed function of improving translation as the modified nucleosides of specific tRNAs (Persson et al 1994) free CKs evolved to have further various specific functions as signalling molecules in plants and organisms interacting with plants. Decomposition of tRNA was thus originaly thought to be a source of free CKs.…”

“…CKs and their functions are not unique to plants. CKs are involved in RNA translation in phyllogeneticaly distinct organisms from bacteria to humans (Persson et al 1994;Golovko et al 2000), and various plant-interacting organisms employ or manipulate CKs to sequester plant developmental programmes to their own ends (Schultz 2002).…”

Identification and functional characterization of the candidate tumor suppressor gene TRIT1 in human lung cancer

“…tRNA-free cytokinins are present in plants where they act as phytohormones to promote and regulate several growth and developmental processes (Miller et al, 1955;Mok, 1994). Cytokinins in their tRNA-bound form are found in several organisms, including mammals (Persson et al, 1994) and represent one of the numerous post-transcriptional modifications of tRNA molecules. At present, 81 different modified residues have been identified that most frequently involve the wobble position (residue 34) and the position 3 0 adjacent to the anticodon (residue 37) (Rozenski et al, 1999).…”

“…All of these modifications have been shown to be essential in maintaining the correct reading frame of the translational machinery, thus improving fidelity and efficiency of protein synthesis and avoiding errors that could be detrimental for cells (Persson, 1993;Bjork et al, 1999;Urbonavicius et al, 2001). N 6 -isopentenyladenosine (i 6 A) is the only known cytokinin existing in animal tRNAs and is specifically found at position 37 of tRNA molecules that bind codons starting with uridine (Persson et al, 1994). Addition of i 6 A on residue 37 of tRNA molecules is catalysed by tRNA-IPTs using W2-dimethylallyl pyrophosphate as donor of the isopentenyl group.…”