Freestanding tRNA editing subunit of threonine--tRNA ligase, the catalytic subunit is probably AC Q9YDW0. Deacylates (edits) mischarged L-seryl-tRNA(Thr) in trans; has no activity on correctly charged L-threonyl-tRNA(Thr) (PubMed:26113036). Probably does not aminoacylate tRNA(Thr) (By similarity). Deacylates correctly charged glycyl-tRNA(Gly), but not glycyl-tRNA(Gly)(2'-dA76) (the terminal 2'-OH of tRNA adenine 76 has been dehydroxylated) nor the 2'-fluoro tRNA derivative, strongly suggesting the editing function is catalyzed by the 2'-OH of A76 of tRNA(Thr) (PubMed:26113036). Probably interacts with its catalytic subunit (By similarity). The N-terminal domain (about residues 1-140) is an archaea-specific tRNA-editing domain (PubMed:26113036) that has a highly similar structure to Dtd (D-aminoacyl-tRNA deacylase). Editing of incorrectly charged L-seryl-tRNA(Thr) by this domain is tRNA catalyzed (PubMed:26113036). There are two ThrRS in this archaeon. The first one (APE_0809.1, AC Q9YDW0) is most similar to bacterial ThrRS but it lacks the N-terminal editing domain. The second one (APE_0117.1, this entry) is most similar to archaeal ThrRS but lacks the central catalytic domain; it probably does not aminoacylate tRNA(Thr). Belongs to the class-II aminoacyl-tRNA synthetase family. Archaea-specific ThrRS editing domain subfamily.