In further studies with a CDK phosphorylation SO2426 deletion mutant under chromate challenge, the so3030-3031-3032 operon was significantly down-regulated [21, 41]. These data, together with the predicted SO2426-binding motif upstream of so3030, suggest that SO2426 directly regulates siderophore production in strain MR-1

under conditions of chromate stress. We employed electrophoretic mobility shift assay (EMSA) selleck to determine if the SO2426 protein was able to interact with the predicted binding sequence upstream of the so3030-3031-3032 operon. Our previous 5′ RACE studies demonstrated that the likely 5′ terminus of SO2426 occurs at a methionine located at position 11 downstream from the originally annotated translation start [21]. Comparative sequence analysis of SO2426 with the CpxR and OmpR amino acid sequences from V. cholerae and E. coli showed that sequence homology between conserved receiver domains for these other well-characterized response regulators and SO2426 begins 13 amino acids downstream of the annotated start site for SO2426 [21]. This conservation is further

find more observed for the Shewanella SO2426 orthologs (Figure 1). In order to test the functionality of the shorter version of SO2426, both the full-length annotated form (designated SO2426) and the “”short”" form beginning with M11 (designated SO2426sh), were expressed using the pTrcHis expression vector system, which incorporates an N-terminal six-histidine tag for affinity purification. The His-tagged proteins were expressed in E. coli and partially purified from crude cell extracts by Ni-affinity column purification (see Methods for details). Expression of the recombinant SO2426 protein was determined by SDS-PAGE (Figure 4A) and Western blotting (Figure 4B), which confirmed the presence of this protein within the expected size range of 26-27.4 kDa. Similar SDS-PAGE and immunoblotting results were obtained for the verification of recombinant SO2426sh expression (data not shown). Figure 4 Partial purification (A) and Western blot (B) verification of recombinant SO2426 protein. Panel A, silver-stained gel of partial purification using a Ni-affinity column. Panel B, Western blot analysis performed in parallel

with Anti-HisG Antibody (Invitrogen). Lanes: 1, MW markers; 2, cell lysate; Carbachol 3, Wash 1; 4, Wash 2; 5-8, Elution Fractions 1-4. Recombinant SO2426 is denoted with an arrow. A digoxigenin-labeled DNA probe spanning the predicted SO2426-binding site motif upstream of the so3030-3031-3032 operon (Figure 5, double underlined region), but excluding the putative Fur box, was generated by PCR amplification and used as the DNA probe in measuring the DNA-binding activity of the partially purified recombinant SO2426 and SO2426sh proteins. Figure 6A shows that the DNA probe shifted upward in the presence of recombinant SO2426, with the shift becoming incrementally more enhanced as the protein concentration in the EMSA reaction mixture was increased.