Figure 4. Schematic illustration of CheA domain organization. CheA is organized into five distict domains: (a) a phosphotransfer domain (HPt), a response regulator binding domain (YB), a dimerization domain (D), a catalytic kinase domain (CA), and a chemoreceptor/CheW binding domain (R). (b) CheA forms a homodimer with the two subunits phosphorylating each other.