The Enzyme Database

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EC 2.7.7.79     
Accepted name: tRNAHis guanylyltransferase
Reaction: p-tRNAHis + ATP + GTP = pppGp-tRNAHis + AMP + diphosphate (overall reaction)
(1a) p-tRNAHis + ATP = App-tRNAHis + diphosphate
(1b) App-tRNAHis + GTP = pppGp-tRNAHis + AMP
Other name(s): histidine tRNA guanylyltransferase; Thg1p (ambiguous); Thg1 (ambiguous)
Systematic name: p-tRNAHis:GTP guanylyltransferase (ATP-hydrolysing)
Comments: In eukarya an additional guanosine residue is added post-transcriptionally to the 5′-end of tRNAHis 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, histidyl-tRNA ligase. The enzyme requires a divalent cation for activity [2]. ATP activation is not required when the substrate contains a 5′-triphosphate (ppp-tRNAHis) [3].
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc
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. tRNAHis maturation: an essential yeast protein catalyzes addition of a guanine nucleotide to the 5′ end of tRNAHis. 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 tRNAHis. 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]
[EC 2.7.7.79 created 2011]
 
 


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