Figure 2. Four different patterns of covalent linkage between the protein domains involved in phosphorelays.

(A) A four protein phosphorelay. (B) A phosphorelay with and hybrid kinase at the beginning of the cascade. (C) A two protein phosphorelay where the first two phosphotransfer steps between domains contained in a single protein. (D) A one protein phosphorelay, where all phosphotransfer steps take place between domains of a single protein.