InterPro

Thg1 was originally characterised as synthesising the guanine nucleotide at the -1 position of the histidinyl tRNA (HtRNA). Thg1 has also been shown to have polymerase activity, which has been proposed to be the ancestral activity of this enzyme [PMID: 20080734, PMID: 16731615].

Thg1 polymerases contain an additional region of conservation C-terminal to the core palm domain that comprise of 5 helices and two strands [PMID: 20591188]. This region has several well-conserved charged residues including a basic residue found towards the end of the first helix of this unit might contribute to the Thg1-specific active site [PMID: 20591188]. This C-terminal module of Thg1 is predicted to form a helical bundle that functions equivalently to the fingers of the other nucleic acid polymerases, probably in interacting with the template HtRNA [PMID: 20591188].