|Superclasses:||Reactions Classified By Conversion Type → Simple Reactions → Chemical Reactions|
|Reactions Classified By Substrate → Macromolecule Reactions → Polynucleotide-Reactions → RNA-Reactions → tRNA-Reactions|
EC Number: 18.104.22.168
The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the Enzyme Commission system.
Mass balance status: Undetermined; a substrate lacks a chemical formula
Enzyme Commission Primary Name: tRNAHis guanylyltransferase
Enzyme Commission Synonyms: histidine tRNA guanylyltransferase, Thg1p (ambiguous), Thg1 (ambiguous)
Enzyme Commission Summary:
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 22.214.171.124, histidyl-tRNA ligase. The enzyme requires a divalent cation for activity [Pande91]. ATP activation is not required when the substrate contains a 5-triphosphate (ppp-tRNAHis) [Gu03].
The enzyme catalyzes two successive reactions.
The overall reaction is:
Gu03: Gu W, Jackman JE, Lohan AJ, Gray MW, Phizicky EM (2003). "tRNAHis maturation: an essential yeast protein catalyzes addition of a guanine nucleotide to the 5' end of tRNAHis." Genes Dev 17(23);2889-901. PMID: 14633974
Hyde10: Hyde SJ, Eckenroth BE, Smith BA, Eberley WA, Heintz NH, Jackman JE, Doublie S (2010). "tRNA(His) guanylyltransferase (THG1), a unique 3'-5' nucleotidyl transferase, shares unexpected structural homology with canonical 5'-3' DNA polymerases." Proc Natl Acad Sci U S A 107(47);20305-10. PMID: 21059936
Jackman08: Jackman JE, Phizicky EM (2008). "Identification of critical residues for G-1 addition and substrate recognition by tRNA(His) guanylyltransferase." Biochemistry 47(16);4817-25. PMID: 18366186
Placido10: Placido A, Sieber F, Gobert A, Gallerani R, Giege P, Marechal-Drouard L (2010). "Plant mitochondria use two pathways for the biogenesis of tRNAHis." Nucleic Acids Res 38(21);7711-7. PMID: 20660484
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