Probable tRNA (His) guanylyltransferase, also known as THG1L, belongs to the tRNA (His) gyanylytransferase family. Localized to the cytoplasm, THG1L is also found near the nuclear membrane and is expressed in many tissues, including liver and lung. Upon DNA damage, THG1L is phosphorylated, most likely by ATM or ATR. It is expressed in a cell cycle-dependent manner and may be involved in cell cycle progression and cell proliferation. Recombinant human THG1L protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.