syringae pv. phaseolicola NPS3121. A 300 bp radiolabeled DNA fragment

(P phtD ), spanning positions -111 to +188 relative to the transcription start site of the phtD operon was used as probe (Figure 1B). Radiolabeled P phtD fragment was incubated with cellular protein extracts from P. syringae pv. phaseolicola NPS3121 grown at 28°C and 18°C under appropriate binding conditions. Mobility shift assays showed that the fragment was able to form a specific DNA-protein complex with a protein found in extracts of cells grown at 18°C (the optimal temperature for toxin production). Likewise, the same retarded mobility GW3965 complex was obtained with extracts from cultures grown at 28°C, indicating that the presence of the interacting protein is independent of temperature (see Additional file 1). Figure 1 Gel shift competition assays. (A) Graphic representation of the pht region. Each arrow represents an QNZ price individual gene, with the direction of the arrow indicating the direction of transcription. Red arrows indicate genes whose function

have been previously reported (B) Detailed view of INK1197 order the phtD operon upstream region indicating the P phtD fragments used as unlabeled DNA competitors. The blue bars represent the probes able to compete the DNA-protein complex, while the red bars represent probes unable to compete the complex. The fragment “”I”" corresponding to the region of 104 bp defined as the binding site for protein. (C) An example of gel shift competition assays used in this case, fragment “”I”" as competitor. These assays were carried out using crude protein extracts of P. syringae pv. phaseolicola NPS3121 grown at 18°C in M9 minimal medium and increasing concentrations of different unlabeled DNA fragments indicated in (B) as competitors. We show the gel shift competition assay performed with the 104 bp probe, which was identified as the minimum region necessary to bind a putative transcription factor. The concentration

of unlabeled DNA competitors was as follows: lanes 1 and 2, no competitor DNA; lane 3, 25 ng (0.36 pmol); lane 4, 50 ng (0.73 pmol); lane 5, 60 ng (0.87 pmol); Tryptophan synthase lane 6, 100 ng (1.46 pmol); lane 7, 150 ng (2.18 pmol); and lane 8, 200 ng (2.9 pmol). To determine the specificity and localization of the observed protein-DNA complex, mobility shift assays were carried out using different P phtD fragments as unlabeled competitors (indicated in Figure 1B). These assays showed that the retarded band was effectively competed by the full-length probe (A) and by fragments B, C, D and I, thus indicating that the observed protein-DNA interaction is located in a 104 bp region that spans positions -111 to -8, relative to the phtD operon transcription start site (Figure 1B and 1C). Although shorter length probes (G, H) were used in gel shift competition assays, these were unable to compete the DNA-protein complex (data not shown).