Explain how retinoblastoma protein works.
The gene for it is widely expressed. In normal cells, the protein is inactivated by phosphorylation and activated by dephosphorylation.
Active (dephosphorylated) pRb binds and inactivates the cellular transcription factor E2F1, the function of which is required for cell cycle progression
In a G0 cell, active RB protien binds to E2F to inactivate the regulatory protien and thus keep the cell from transcribing
In a proliferating, cell, Rb is phosphorylated; and, it releases the protein, allowing it to activate transcription