Part of a heterotetrameric complex that catalyzes the two-step biosynthesis of anthranilate, an intermediate in the biosynthesis of L-tryptophan. In the first step, the glutamine-binding beta subunit of anthranilate synthase (AS) provides the glutamine amidotransferase activity which generates ammonia as a substrate that, along with chorismate, is used in the second step, catalyzed by the large alpha subunit of AS to produce anthranilate. Plays an important regulatory role in auxin production via the tryptophan-dependent biosynthetic pathway. chorismate + L-glutamine = anthranilate + H(+) + L-glutamate + pyruvate Binds 1 Mg(2+) ion per subunit. Feedback inhibition by tryptophan. Amino-acid biosynthesis; L-tryptophan biosynthesis; L-tryptophan from chorismate: step 1/5. Heterotetramer consisting of two non-identical subunits: a beta subunit and a large alpha subunit. A number of isoforms are produced. According to EST sequences. Expressed in the central cylinder of mature primary root zones, including pericycle and early lateral root primordia, and vasculature of cotyledons. By ethylene, methyl jasmonate (MeJa), wounding and infection by a virulent strain of P.syringae pv maculicola. No visible phenotype under normal growth conditions, but mutant plants are insensitive to inhibition of root elongation by ethylene, resistant to the herbicide and anthranilate analog 6-methylanthranilate, resistant to growth inhibition by the tryptophan analog alpha-methyltryptophan and insensitive to feedback inhibition by tryptophan. Belongs to the anthranilate synthase component I family.