Chemotaxis in Escherichia coli: associations of protein components

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Abstract
Interactions between protein components of the chemotaxis mechanism in E. coli were investigated by using the cleavable cross-linking reagent, dithiobis(succinimidyl propionate). Two methods were used to allow detection of chemotaxis-specific proteins in intact cells. The 1st method was to program their synthesis in the presence of [35S]methionine using .lambda. E. coli hybrid phages which carry the chemotaxis genes. The 2nd method was to label endogenous methyl-accepting chemotaxis proteins (MCP), with the methyl donor S-adenosyl-L-[methyl-3H]methionine, after permeabilizing the cells with EGTA [ethyleneglycol-bis(.beta.-aminoethyl ether)N,N,N'',N''-tetraacetate]. Physical associations between proteins were analyzed, after cross-linking, by 2-dimensional NaDodSO4[sodium dodecyl sulfate]-polyacrylamide gel electrophoresis. Both labeling methods demonstrate that MCP I and MCP II exist as functional tetramers. Other proteins involved with chemotaxis formed dimers and higher polymers. Phage-directed products of cheW, cheX, motA and cheA formed dimers. CheB and hag products formed multimers. A number of apparent interactions between different gene products were detected as well. Products of cheB, cheW, cheZ, motA and motB formed complexes with other gene products. Included are results consistent with interactions between the products of cheB and cheZ.