Retinoblastoma-binding protein 5 (RbBP5) is a ubiquitously expressed nuclear protein that contains WD40 repeat-like domains. RbBP5 binds directly to tumor suppressor retinoblastoma protein (RB) and regulates cell proliferation. Interaction of RbBP5 occurs preferentially with underphosphorylated RB through the E1A-binding pocket B. RbBP5 is also an important component of the multi-subunit SET1 lysine methyltransferase protein complex, which includes MLL1. RbBP5 interacts directly with WDR5 contributing to the activation of the MLL1 core protein complex. MLL1-4 protein complexes catalyze the di- and trimethylation of histone H3 at lysine 4 (H3K4me2/me3), leading to the maintenance of global H3K4 trimethylation.
