Localization of components of the chemotaxis machinery of Escherichia coli using fluorescent protein fusions

We prepared fusions of yellow fluorescent protein [the YFP variant of green fluorescent protein (GFP)] with the cytoplasmic chemotaxis proteins CheY, CheZ and CheA and the flagellar motor protein FliM, and studied their localization in wild-type and mutant cells of Escherichia coli. All but the CheA fusions were functional. The cytoplasmic proteins CheY, CheZ and CheA tended to cluster at the cell poles in a manner similar to that observed earlier for methyl-accepting chemotaxis proteins (MCPs), but only if MCPs were present. Co-localization of CheY and CheZ with MCPs was CheA dependent, and co-localization of CheA with MCPs was CheW dependent, as expected. Co-localization with MCPs was confirmed by immunofluorescence using an anti-MCP primary antibody. The motor protein FliM appeared as discrete spots on the sides of the cell. These were seen in wild-type cells and in a fliN mutant, but not in flhC or fliG mutants. Co-localization with flagellar structures was confirmed by immunofluorescence using an antihook primary antibody. Surprisingly, we did not observe co-localization of CheY with motors, even under conditions in which cells tumbled.