Strong and regulated promoters in the cyanobacterium Anabaena PCC 7120.

The strengths of several promoters were assessed in the cyanobacterium Anabaena PCC 7120 by fusing them to luxAB, encoding bacterial luciferase. Two promoters, Ptac and PpsbA, with sequences nearly identical to consensus Escherichia coli sigma 70 promoters, gave as high or higher expression than the strong Anabaena promoter, Prbc. Pnpt, the natural promoter driving expression of the kanamycin-resistance determinant from Tn5, was poorly expressed in Anabaena. The Lac repressor partially repressed expression from Ptac, permitting regulated expression in Anabaena after induction with isopropyl thiogalactoside to a level 4-5-fold higher than without inducer.