ID 2.7.7.79 DE tRNA(His) guanylyltransferase. AN Histidine tRNA guanylyltransferase. CA p-tRNA(His) + ATP + GTP + H(2)O = pG-P-tRNA(His) + AMP + 2 diphosphate. CC -!- In eukarya an additional guanosine residue is added post- CC transcriptionally to the 5'-end of tRNA(His) molecules. CC -!- The addition occurs opposite a universally conserved adenosine(73) CC and is thus the result of a non-templated 3'-5' addition reaction. CC -!- The additional guanosine residue is an important determinant for CC aminoacylation by EC 6.1.1.21. CC -!- The enzyme requires a divalent cation for activity. CC -!- ATP activation is not required when the substrate contains a CC 5'-triphosphate (ppp-tRNA(His)). DR F4IRQ5, THG1_ARATH ; Q75DJ3, THG1_ASHGO ; Q05B50, THG1_BOVIN ; DR Q6FPX3, THG1_CANGA ; Q6BKD4, THG1_DEBHA ; Q54E29, THG1_DICDI ; DR Q9V3N8, THG1_DROME ; Q9NWX6, THG1_HUMAN ; Q6CW75, THG1_KLULA ; DR Q9CY52, THG1_MOUSE ; Q7SDM8, THG1_NEUCR ; Q5M965, THG1_RAT ; DR Q9Y7T3, THG1_SCHPO ; P53215, THG1_YEAST ; F4ISV6, THG2_ARATH ; //