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TGS (ThrRS, GTPase and SpoT) domain structurally similar to a beta-grasp ubiquitin-like fold This family includes eukaryotic and some bacterial threonyl-tRNA synthetases (ThrRSs), a distinct Obg family GTPases, and guanosine polyphosphate hydrolase (SpoT) and synthetase (RelA), which are involved in stringent response in bacteria, as well as uridine kinase (UDK) from Thermotogales. All family members contain a TGS domain named after the ThrRS, GTPase, and SpoT/RelA proteins where it occurs. It is a small domain with a beta-grasp ubiquitin-like fold, a common structure involved in protein-protein interactions. The functions of the TGS domain remains unclear, but its presence in two types of regulatory proteins (the GTPases and guanosine polyphosphate phosphohydrolases/synthetases) suggests a ligand (most likely nucleotide)-binding, with a regulatory role.
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