<p> The TGS domain is present in a number of enzymes, for example, in threonyl-tRNA synthetase (ThrRS), GTPase, and guanosine-3',5'-bis(diphosphate) 3'-pyrophosphohydrolase (SpoT) [<cite idref="PUB00007363"/>]. The TGS domain is also present at the amino terminus of the uridine kinase from the spirochaete <taxon tax_id="160">Treponema pallidum</taxon> (but not any other organism, including the related spirochaete <taxon tax_id="139">Borrelia burgdorferi</taxon>). </p><p>TGS is a small domain that consists of ~50 amino acid residues and is predicted to possess a predominantly beta-sheet structure. There is no direct information on the functions of the TGS domain, but its presence in two types of regulatory proteins (the GTPases and guanosine polyphosphate phosphohydrolases/synthetases) suggests a ligand (most likely nucleotide)-binding, regulatory role [<cite idref="PUB00007363"/>]. </p>