Figure 1.

Repression of the tra box promoter of pPBL1 depends on TraR and AAI. E. coli DH5α(pPBL1) harboring pZLQR as a source of TraR was grown in A medium to a density of about 10⁷ clony-forming units/ml. At t = 0, the culture was split into three subcultures. IPTG (100 μM) was added to two subcultures to induce expression of traR (○, ▵). After 2 hours of incubation (arrow), AAI (25 nM) was added to the third subculture (▴) and to one of the two subcultures previously induced with IPTG (▵). Incubation was continued, growth was followed by using Klett colorimetry (♦), and samples were taken from each culture at the times indicated and assayed for β-galactosidase activity.