TRNA(His) guanylyltransferase

tRNA(His) guanylyltransferase (, histidine tRNA guanylyltransferase, Thg1p, Thg1) is an enzyme with systematic name p-tRNA(His):GTP guanylyltransferase (ATP-hydrolysing). This enzyme catalyses the following chemical reaction


 * p-tRNA(His) + ATP + GTP $$\rightleftharpoons$$ pppGp-tRNA(His) + AMP + diphosphate (overall reaction)
 * (1a) p-tRNA(His) + ATP $$\rightleftharpoons$$ App-tRNA(His) + diphosphate
 * (1b) App-tRNA(His) + GTP $$\rightleftharpoons$$ pppGp-tRNA(His) + AMP

The enzyme requires a divalent cation for activity.