HBZ interacts with the B pocket of hypophosphorylated retinoblastoma (Rb) protein. (a) Interaction between Rb and wild-type HBZ and the HBZ deletion mutants. Schematic diagrams of the HBZ mutants are shown at the bottom. (b) Interaction between endogenous Rb and HBZ in MT4 cells. (c) Interaction between HBZ and wild-type Rb and Rb deletion mutants. Schematic diagrams of the Rb mutants are shown at the bottom. (d) HBZ preferentially binds to hypophosphorylated Rb. Expression vectors for the indicated proteins were transfected into 293FT cells, and protein interactions were analyzed by immunoprecipitation (IP). AD, activation domain; CD, central domain; NT, N terminus; WT, wild type. Representative data of three independent experiments are shown.