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) (PubMed:15240874). Also activates L-serine, but does not detectably transfer it to tRNA(Thr) (PubMed:15240874). Edits incorrectly charged L-seryl-tRNA(Thr) via its editing domain (PubMed:15240874). Has no activity on correctly acylated L-seryl-tRNA(Ser) or L-threonyl-tRNA(Thr) (PubMed:15240874). 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 tRNA catalyzed (PubMed:26113036). ATP + L-threonine + tRNA(Thr) = AMP + diphosphate + H(+) + L-threonyl-tRNA(Thr) Binds 1 zinc ion per subunit. Not inhibited by 1 uM borrelidin (BN); probably does not bind BN. kcat is 12.3 sec(-1) for L-serine, 13.5 for L-threonine at 60 degrees Celsius (PubMed:15240874). kcat is 1.2 sec(-1) (PubMed:15507440). Homodimer. The N-terminal domain (about residues 1-140) is an archaea-specific tRNA-editing domain (PubMed:15240874, 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). Belongs to the class-II aminoacyl-tRNA synthetase family. Extended N-terminus.