Abstract - 2qgnA

tRNA isopentenyltransferase (tRNA-IPT) is an important enzyme that catalyses the biosynthesis of cytokinins. Cytokinins are modified adenine which can be present in the tRNA-free or tRNA-bound form. Such modification at specific position of the target tRNA influences its molecular function. This family of enzyme is conserved in all organisms including plants, microorganisms and higher eukaryotes. The structure of this protein is first determined in Bacillus halodurans and the human tRNA-IPT has been recently cloned. The latter is found to have a C2H2 zinc finger motif which is also found in other organisms except prokaryotes. Structure-based alignment of tRNA isopentenyl transferase with other neighbourhood proteins has shown many similar physical properties proposing that these proteins may be functionally related. Conserved residues found across different species with multiple sequence alignment indicates the possibility that these proteins may have evolved from the same ancestors. Interestingly,the human sequence was found to contain a single C2H2 Zn-finger-like motif, which was detected also in yeast, and several putative tRNA transferases located by BLAST searches, but not in prokaryotic homologues. It is possible that this motif is a result of evolution. Employing various bioinformatics tools such as Profunc, Interpro, CATH, STRING, CASTp, Blast, ClustalX and PDB, three important aspects of this enzyme was revealed - the structure, function and evolution.