RB1 and neoplasm: The G1-S progression of the cell division cycle was also limited by increased expression of retinoblastoma protein 1 (Rb1, Fig. 13a9), which acts as a tumour repressor because it binds and inhibits the transcription activating complexes of E2 promoter-binding–protein-dimerization partners (E2F-DP) insomuch as to restrict the Nrf1α−/− cells to enter the S phase, as described elsewhere76.