Probable tRNA（His) guanylyltransferase（THG1L) is a member of the tRNA（His) gyanylytransferase family. THG1L which is localized to the cytoplasm also found adjacent to the nuclear membrane and expressed in various tissues， including liver and lung. THG1L is expressed in a cell cycle-dependent manner and may be involved in cell cycle progression and cell proliferation. THG1L adds a GMP to the 5’-end of tRNA（His) after transcription and RNase P cleavage. This step is vital for accurate recognition of the tRNA and for the fidelity of protein synthesis. Upon DNA damage， THG1L is phosphorylated， presumably by ATM or ATR.
