Promoter regions characterized in this work. (A) Fragment of the promoter region of csnN106 gene variants. Pr-WT: native promoter region, the putative -35 and -10 boxes are indicated in blue. Pr-Ph: a construct in which the native promoter has been replaced by a double promoter from Streptomyces ghanaensis phage I19, the respective -35 and -10 boxes are over and underlined. Low case letters indicate nucleotide changes between Pr-WT and Pr-PH. (*): start points of transcription. Arrows: inverted repeats of the palindromic box. (B) Alignment of palindromic sequences present in the promoter regions of chitosanase genes in actinomycetes. Nucleotides are numbered relative to the center of symmetry. In the consensus sequence, nucleotides are coloured according to their importance for DNA-protein interaction established by equilibrium competition experiments : red: nucleotides critical for interaction; green: nucleotides moderately important for interaction; black: nucleotides without apparent effect on interaction. (↑): base pairs mutated in the Pr-Pa construct. GH: glycoside hydrolase family.