Figure 3

Functional role of the URE region. (A) Schematic representation of PstyA and its mutated derivatives cloned in the promoter probe vector pPR9TT. Plasmid designations are given on the left. Red inverted arrows indicate the StyR-P binding sites. The IHF binding site is blue-boxed. Nucleotides numbering is referred to the PstyA transcription start site. The white rectangle indicates the styA ORF. The grey arrow indicates the lacZ gene fused to styA. A detail of the URE region is reported on the top. Asterisks and triangles indicate nucleotides mutated (A→T and T→A substitutions) to generate the pPR9STY1mut and pPR9IHFmut constructs, respectively. (B) β-galactosidase activities disclosed by P. fluorescens ST strains carrying the different pPR9TT-derivative plasmids represented in (A). Filled symbols, pPR9Pa 1; open symbols, pPR9STY1mut; diamonds, cultures growing on styrene; circles, styrene-grown precultures to which both styrene and 0.4% glucose were added at time zero; triangles, styrene-grown precultures to which only 0.4% glucose was added at time zero. (C) β-galactosidase activities measured after two exponential cell divisions on styrene (white bars), on styrene plus 0.4% (wt/vol) glucose (grey bars), or on 0.4% (wt/vol) glucose (black bars), are reported in the histogram. The extent of glucose mediated repression in carbon catabolite repression condition is indicated by the double arrow line. Repression was calculated by assuming that the promoter activity in styrene was 100% and the promoter activity in glucose corresponded to 100% repression. Standard deviations (vertical lines) are based on the mean values of five independent experiments.