CHEC AND CHED INTERACT TO REGULATE METHYLATION OF BACILLUS-SUBTILIS METHYL-ACCEPTING CHEMOTAXIS PROTEINS

In this study, we have demonstrated that two unique proteins in Bacill us subtilis chemotaxis, CheC and CheD, interact. We have shown this in teraction both by using the yeast two-hybrid system and by precipitati on of in vitro translated products using glutathione-S-transferase fus ions and glutathione agarose beads. We have also shown that CheC inhib its B. subtilis CheR-mediated methylation of B. subtilis methyl-accept ing chemotaxis proteins (MCPs) but not of Escherichia coil MCPs. It wa s previously reported that cheC mutants tend to swim smoothly and do n ot adapt to addition of attractant; cheD mutants have very poorly meth ylated MCPs and are very tumbly, similar to cheA mutants. We hypothesi ze that CheC exerts its effect on MCP methylation in B. subtilis by co ntrolling the binding of CheD to the MCPs. In absence of CheD, the MCP s are poor substrates for CheR and appear to tie up, rather than activ ate, CheA. The regulation of CheD by CheC may be part of a unique adap tation system for chemotaxis in B. subtilis, whereby high levels of Ch eY-P brought about by attractant addition would allow CheC to interact with CheD and consequently leave the MCPs, reducing CheA activity and hence the levels of CheY-P.