Gene expression in Pseudomonas

Gene regulation studies in pseudomonad bacteria are mainly restricted to Pseudomonas aeruginosa and Pseudomonas putida. Constitutive promoters exhibit DNA sequences similar to the σ (70)-dependent constitutive promoters of Escherichia coli. The TOL meta-cleavage pathway operon promoter and the nah operon promoters are the best characterized σ (70)-dependent promoters, which exhibit-10 regions rich in As and Ts and non-conserved-35 regions. The DNA binding motif recognized by the respective positive regulators lies between-40 and-80. Another set of positively controlled promoters exhibit upstream activator sequences located between-100 and-500. Transcription stimulation from some of these promoters also involves σ (54) and/or IHF protein. In this class of promoters, DNA binding is required to establish open complexes. Promoters for the utilization of histidine (hut) are under negative control by the HutC protein. hut promoters exhibit-10/-35 consensus regions and an overlapping operator sequence between-15 and-50. Repression of hut promoters seems to be achieved through steric hindrance of RNA polymerase. Another set of promoters are controlled by catabolite repression, which seems to be cyclic-AMP independent.