The protocol for the ChIP assay was based

on the methods used by Strahl-Bolsinger et al. (1997), with some modifications. Fifty milliliter of LB broth were inoculated with 2.5 mL of overnight cultures and incubated at 37 °C with shaking. At an OD600 nm of approximately 1.0, 1% formaldehyde was added and samples were incubated for 15 min at room temperature. Glycine (125 mM) was added and the mixture was incubated for 5 min at room temperature. Cells were pelleted and washed once with 1 × phosphate-buffered saline (PBS) buffer (1.5 mM KH2PO4, 137 mM NaCl, 8 mM Na2HPO4, pH 7.2) and resuspended in 300 μL ChIP lysis buffer [50 mM HEPES pH 7.5, 140 mM CX 5461 NaCl, 1% Triton X100, 0.1% sodium deoxycholate, plus one Complete-Mini protease inhibitor cocktail tablet (Roche)]. Glass beads were then added and the mixture was incubated with shaking for 30 min at 4 °C at the maximum level. Glass beads were removed by brief centrifugation and the cell suspension was sonicated PR-171 mw for 30 s (3.5 peak–peak amplitude, Branson Sonifier 450). Samples were pelleted (4 °C) and supernatants were transferred to new tubes. A 15-μL aliquot of each sample was set aside at this point to use later as total DNA samples. Two microliters of anti-TraJ or anti-TraK antibodies (both diluted 1 : 20 000)

were added to 750 μL of the supernatant and the mixtures were incubated for 2 h with shaking at 4 °C. Protein A beads (50 μL), previously washed with ChIP lysis buffer, were added and incubated for 4 h with shaking at 4 °C. Immunoprecipitates were washed twice with 1 mL ChIP lysis buffer, twice with 1 mL ChIP high-salt lysis buffer (ChIP lysis buffer with 500 mM NaCl), twice with 1 mL ChIP wash buffer (10 mM Tris pH 8, 250 mM LiCl, 0.5% NP-40, 0.5% Na deoxycholate, 1 mM EDTA) and twice with 1 mL TE buffer. Samples were eluted by adding 75 μL elution buffer (50 mM Tris pH 8, 1% SDS,

10 mM EDTA) twice, and the beads were incubated for 10 min at 65 °C. Both elutions were combined and incubated overnight at 65 °C. Samples were then purified using the Qiagen PCR purification kit and eluted with 50 μL ddH2O. Eluted DNA was serially diluted with ddH2O. One microliter aliquots of these DNA dilutions were analyzed in a standard 25 μL PCR reaction, using primers specific for the promoter region of traY (RWI91–RWI92), selleck chemical to produce a 200-bp fragment by Vent DNA polymerase (Table 2). PCR products were run on a 1.5% agarose gel, stained with ethidium bromide and photographed under UV light. The protocol for the cross-linking was based on the methods used by Klimke et al. (2005), with some modifications. LB broth (3.0 mL) containing 0.1% arabinose was inoculated with 0.15 mL of MC4100/FlactraJ90/pBADTraJ overnight cultures and grown at 37 °C to an OD600 nm of approximately 1.0. Pellets from two 1-mL aliquots per culture were washed three times with PBS buffer and resuspended in 200 μL PBS. One sample was cross-linked with 0.5 mM DSS, whereas the second was used as a negative control.