Catalyzes the attachment of threonine to tRNA(Thr) in a two-step reaction: L-threonine is first activated by ATP to form Thr-AMP and then transferred to the acceptor end of tRNA(Thr) (Probable). Edits incorrectly charged L-seryl-tRNA(Thr) via its editing domain (PubMed:16902403, PubMed:21098258). Deacylates correctly charged glycyl-tRNA(Gly), but neither glycyl-tRNA(Gly)(2'-dA76) (the terminal 2'-OH of tRNA(Thr) adenine 76 has been replaced by hydrogen) nor the 2'-fluoro tRNA derivative do so, strongly suggesting the editing function is tRNA catalyzed (PubMed:26113036). ATP + L-threonine + tRNA(Thr) = AMP + diphosphate + H(+) + L-threonyl-tRNA(Thr) Binds 1 zinc ion per subunit. Homodimer. The N-terminal domain (about residues 1-143) is an archaea-specific tRNA-editing domain (PubMed:16902403) that has a highly similar structure to Dtd (D-aminoacyl-tRNA deacylase); the domain binds L-serine and L-cysteine and most D-amino acids but not L-threonine (PubMed:15908961, PubMed:16902403). Editing of incorrectly charged L-seryl-tRNA(Thr) by this domain is tRNA catalyzed (PubMed:16902403, PubMed:21098258, PubMed:26113036). Belongs to the class-II aminoacyl-tRNA synthetase family.