Catalyzes the attachment of L-alanine to tRNA(Ala) in a two-step reaction: L-alanine is first activated by ATP to form Ala-AMP and then transferred to the acceptor end of tRNA(Ala). AlaRS also incorrectly activates the sterically smaller amino acid glycine as well as the sterically larger amino acid L-serine; generates 2-fold more mischarged Gly than Ser (PubMed:28362257). These mischarged amino acids occur because the of inherent physicochemical limitations on discrimination between closely related amino acids (Ala, Gly and Ser) in the charging step. Edits mischarged Ser-tRNA(Ala) and Gly-tRNA(Ala) but not incorrectly charged Ser-tRNA(Thr) (PubMed:12554667, PubMed:18723508). Dtd edits Gly-tRNA(Ala) 4-fold better than does AlaRS (PubMed:28362257). Attaches Ala to transfer-messenger RNA (tmRNA, also known as 10Sa RNA, the product of the ssrA gene). tmRNA plays a major role in rescue of stalled ribosomes via trans-translation. ATP + L-alanine + tRNA(Ala) = AMP + diphosphate + L-alanyl-tRNA(Ala) Binds 1 zinc ion per subunit; it is not clear where this binding occurs. Homotetramer. Consists of three domains; the N-terminal catalytic domain, the editing domain and the C-terminal C-Ala domain. The editing domain removes incorrectly charged amino acids, while the C-Ala domain, along with tRNA(Ala), serves as a bridge to cooperatively bring together the editing and aminoacylation centers thus stimulating deacylation of misacylated tRNAs. The editing domain removes incorrectly charged amino acids, i.e. Ser-tRNA(Ala) or Gly-tRNA(Ala) become uncharged tRNA(Ala) and the amino acid. It is specific for the acceptor stem of tRNA(Ala). The C-terminal C-Ala domain, along with tRNA(Ala), serves as a bridge to cooperatively bring together the editing and aminoacylation centers thus stimulating deacylation of misacylated tRNAs. This C-Ala domain can be replaced in vitro by the corresponding domain of Aquifex aeolicus or man. Recognition of tRNA(Ala) by the 2 domains is independent, that is one enzyme recognizes the same tRNA(Ala) in 2 different manners. Belongs to the class-II aminoacyl-tRNA synthetase family.