For the negative control, purified FliI was digested for 10 minutes
at 37°C using Proteinase K (Invitrogen). Also, as a negative control, another GST-tagged protein (CopN) known not to have ATPase activity was purified in the same manner and tested for activity. ATPase activity was expressed as μmol phosphate released min-1 mg-1 of protein, and all experiments were performed in triplicate. GST Pull-down Assays To examine the interaction of the flagellar proteins, GST pull-down assays were performed as described AZD5582 mouse previously with the following modifications . Briefly, glutathione agarose beads (30 μL) bound to fifty nanograms of GST tagged FliI, Cpn0859, or FlhA was used in the assay. The beads were incubated overnight at 4°C with the E. coli lysate expressing the His-tagged proteins. The beads were collected by centrifugation and washed with increasing concentrations of NaCl to eliminate spurious protein interactions. All proteins were eluted from the Glutathione
beads and electrophoresed on an 11% SDS-PAGE gel Nutlin-3a before being probed for His-tagged protein. As a negative control, GST alone was incubated on beads with the E. coli lysates. Bacterial-2-Hybrid Assay The bacterial-2-hybrid assay uses protein-protein interactions to bring two fragments VX-680 nmr of adenylate cyclase catalytic domain together to produce cAMP, stimulating β-galactosidase activity. β-galactosidase activity is therefore a representation of protein interaction. This protocol was performed as described by Karimova et al, 2005 . Briefly, E. coli DHP-1 cells (an adenylate cyclase deficient
cell line) were transformed using pT18-FliI/pT18-FlhA/pT18-FliF and either pT25-FlhA or pT25-FliF and selected with 100 μg/μL ampicillin and 34 μg/μL chloramphenicol. Three individual colonies were selected from each plate and grown overnight in 3.0 mL of LB at 30°C in the presence of 0.5 mM IPTG plus appropriate antibiotics. Overnight culture (200 μL) was diluted 1 in 5 into M63 buffer (75 mM (NH4)2SO4, 110 mM KH2PO4, 200 mM K2HPO4, 5 mM FeSO4-7H2O) and the optical density at 600 nm was recorded. The cells were permeabilized using 0.01% Toluene and 0.01% SDS. For the reaction, 50 μL of the permeabilized STK38 cells were diluted into 450 μL of LB broth. The diluted cells were then added to 500 μL of PM2 (70 mM Na2HPO4-H2O, 30 mM NaHPO4-H2O, 1 mM MgSO4, and 0.2 mM MnSO4) buffer containing 100 mM β-mercaptoethanol. The reaction was initiated by adding 250 μL of 12 mg/mL ortho-nitrophenyl-β-galactoside and allowed to continue for 15 seconds at 28°C. The reaction was stopped by the addition of 500 μL of 1.0 M Na2CO3. The absorbance was measured at 420 nm and the β-galactosidase activity was expressed as units of β-galactosidase activity per milligram of bacteria.