Functions in trans to edit the amino acid moiety from mischarged charged Ser-tRNA(Ala). Has little activity against Gly-tRNA(Ala). Binds 1 zinc ion per subunit; the homodimer seems not to bind zinc. The zinc is probably not catalytic (PubMed:16087889). Another report suggests the zinc is catalytic (PubMed:16374837). Monomer and homodimer; the dimer is less active in tRNA editing and does not have a zinc ion associated with it (PubMed:16087889). Another report shows only a monomeric form (PubMed:16374837). Belongs to the class-II aminoacyl-tRNA synthetase family. Editing domain AlaX-S subfamily.