AEROBIC REPRESSION OF THE RHODOBACTER-CAPSULATUS BCHC PROMOTER INVOLVES COOPERATIVE INTERACTIONS BETWEEN CRTJ BOUND TO NEIGHBORING PALINDROMES

Previous studies demonstrated that bacteriochlorophyll, carotenoid, an d light harvesting gene expression in Rhodobacter capsulatus is repres sed under aerobic growth conditions by the repressor CrtJ. Isolated Cr tJ is known to bind to the palindrome TGTN(12)ACA, which is present in two copies in the bchC promoter, one of which spans the -35 and the o ther the -10 sigma-70 recognition sequences. In this study, we demonst rate that CrtJ binds to the two palindromic sites in the bchC promoter in a cooperative manner. The level of cooperativity of CrtJ binding t o the -35 palindrome was shown to be 26-fold. A distance of 8 base pai rs between the two palindromic sites was shown to be critical for coop erative binding, as evidenced by the disruption of binding that result ed when +6 and +11 base pairs were inserted between the palindromes.