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). Also edits incorrectly charged L-seryl-tRNA(Thr). ATP + L-threonine + tRNA(Thr) = AMP + diphosphate + H(+) + L-threonyl-tRNA(Thr) Binds 1 zinc ion per subunit. Homodimer. The N-terminal domain is an archaea-specific tRNA-editing domain that hydrolyzes incorrectly charged L-seryl-tRNA(Thr). Catalysis of tRNA editing is performed by the charged tRNA itself. Belongs to the class-II aminoacyl-tRNA synthetase family.