Catalyzes the biosynthesis of 4-amino-4-deoxychorismate (ADC) from chorismate and glutamine. Required for the synthesis of 4-aminobenzoate (PABA), an important component in tetrahydrofolate biosynthesis. chorismate + L-glutamine = 4-amino-4-deoxychorismate + L-glutamate Cofactor biosynthesis; tetrahydrofolate biosynthesis; 4-aminobenzoate from chorismate: step 1/2. The PABA component provides the glutamine amidotransferase activity. The PABB component catalyzes the formation of ADC by binding chorismate and ammonia. Present with 1550 molecules/cell in log phase SD medium. In the C-terminal section; belongs to the anthranilate synthase component I family.