Part of a heterotetrameric complex that catalyzes the two-step biosynthesis of anthranilate, a precursor for Pseudomonas quinolone signal (2-heptyl-3-hydroxy-4-quinolone; PQS) production which is required to induce the genes for the biosynthesis of the virulence factor pyocyanine (PCN), a characteristic blue-green phenazine pigment produced by P.aeruginosa (PubMed:11591691, PubMed:2153661, PubMed:23449919). In the first step, the glutamine-binding beta subunit (PhnB) 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 (PhnA) to produce anthranilate (By similarity). chorismate + L-glutamine = anthranilate + H(+) + L-glutamate + pyruvate Binds 1 Mg(2+) ion per subunit. Secondary metabolite biosynthesis; pyocyanine biosynthesis. Heterotetramer consisting of two non-identical subunits: a beta subunit (PhnB) and a large alpha subunit (PhnA). Expression increases as cell grow from early to late log phase and further increases in stationary phase; there is about 10-fold more mRNA in stationary than early log phase. Disruption of phnA alone yields 22-34% pyocyanine. Double trpE-phnA disruption requires anthranilate or L-tryptophan for growth on minimal medium and does not make pyocyanine (PubMed:2153661). Double phnA-phnB deletions are tryptophan prototrophs; they make less PQS (PubMed:23449919). PhnAB is not feedback inhibited by tryptophan. The sequence shown is that of strain PAO. Belongs to the anthranilate synthase component I family.