EC 2.7.7.79

Reaction: p-tRNA^His + ATP + GTP + H₂O = pGp-tRNA^His + AMP + 2 diphosphate (overall reaction)
(1a) p-tRNA^His + ATP = App-tRNA^His + diphosphate
(1b) App-tRNA^His + GTP = pppGp-tRNA^His + AMP
(1c) pppGp-tRNA^His + H₂O = pGp-tRNA^His + diphosphate

Glossary: p-tRNA^His = 5'-phospho-ribonucleotide-[tRNA^His]
pGp-tRNA^His = 5'-phospho-guanosine-ribonucleotide-[tRNA^His]
App-tRNA^His = 5'-(5'-diphosphoadenosine)-ribonucleotide-[tRNA^His]
pppGp-tRNA^His = 5'-triphospho-ribonucleotide-[tRNA^His]

Other name(s): histidine tRNA guanylyltransferase; Thg1p (ambiguous); Thg1 (ambiguous)

Systematic name: p-tRNA^His:GTP guanylyltransferase (ATP-hydrolysing)

Comments: In eukarya an additional guanosine residue is added post-transcriptionally to the 5'-end of tRNA^His molecules. The addition occurs opposite a universally conserved adenosine⁷³ and is thus the result of a non-templated 3'-5' addition reaction. The additional guanosine residue is an important determinant for aminoacylation by EC 6.1.1.21, histidine—tRNA ligase. The enzyme requires a divalent cation for activity [2]. ATP activation is not required when the substrate contains a 5'-triphosphate (ppp-tRNA^His) [3].

Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, PDB, CAS registry number:

References:

1. Jahn, D. and Pande, S. Histidine tRNA guanylyltransferase from Saccharomyces cerevisiae. II. Catalytic mechanism. J. Biol. Chem. 266 (1991) 22832-22836. [PMID: 1660462]

2. Pande, S., Jahn, D. and Soll, D. Histidine tRNA guanylyltransferase from Saccharomyces cerevisiae. I. Purification and physical properties. J. Biol. Chem. 266 (1991) 22826-22831. [PMID: 1660461]

3. Gu, W., Jackman, J.E., Lohan, A.J., Gray, M.W. and Phizicky, E.M. tRNA^His maturation: an essential yeast protein catalyzes addition of a guanine nucleotide to the 5' end of tRNA^His. Genes Dev. 17 (2003) 2889-2901. [PMID: 14633974]

4. Placido, A., Sieber, F., Gobert, A., Gallerani, R., Giege, P. and Marechal-Drouard, L. Plant mitochondria use two pathways for the biogenesis of tRNA^His. Nucleic Acids Res. 38 (2010) 7711-7717. [PMID: 20660484]

5. Jackman, J.E. and Phizicky, E.M. Identification of critical residues for G-1 addition and substrate recognition by tRNA(His) guanylyltransferase. Biochemistry 47 (2008) 4817-4825. [PMID: 18366186]

6. Hyde, S.J., Eckenroth, B.E., Smith, B.A., Eberley, W.A., Heintz, N.H., Jackman, J.E. and Doublie, S. tRNA(His) guanylyltransferase (THG1), a unique 3'-5' nucleotidyl transferase, shares unexpected structural homology with canonical 5'-3' DNA polymerases. Proc. Natl. Acad. Sci. USA 107 (2010) 20305-20310. [PMID: 21059936]