FrzE of Myxococcus xanthus is Homologous to Both CheA and CheY of Salmonella typhimurium

Myxococcus xanthus exhibits multicellular development. The "frizzy" (frz) mutants are unable to complete the developmental pathway. Instead of forming fruiting bodies, these mutants form tangled filaments of cells. We have previously shown that four of the frz gene products are homologous to enteric chemotaxis proteins and have proposed that the frz genes constitute a signal-transduction pathway that controls the frequency at which cells reverse their gliding direction. We show here that frzE encodes a protein with a calculated molecular mass of 83 kDa. FrzE is homologous to both CheA and CheY of Salmonella typhimurium, which are members of a family of "two-component response regulators." It is thought that the modulator components autophosphorylate and transfer a phosphate group to their cognate effector components. FrzE contains an unusual (alanine plus proline)-rich region that might constitute a flexible hinge facilitating phosphate transfer between functional domains. We suggest that FrzE is a second messenger that relays information between the signaling protein FrzCD and the gliding motor.