Tumor suppressor that is a key regulator of the G1/S transition of the cell cycle (PubMed:8336704).
The hypophosphorylated form binds transcription regulators of the E2F family, preventing transcription of E2F-responsive genes. Both physically blocks E2Fs transactivating domain and recruits chromatin-modifying enzymes that actively repress transcription. Cyclin and CDK-dependent phosphorylation of RB1 induces its dissociation from E2Fs, thereby activating transcription of E2F responsive genes and triggering entry into S phase. RB1 also promotes the G0-G1 transition upon phosphorylation and activation by CDK3/cyclin-C. Directly involved in heterochromatin formation by maintaining overall chromatin structure and, in particular, that of constitutive heterochromatin by stabilizing histone methylation (PubMed:15750587).
Recruits and targets histone methyltransferases SUV39H1, KMT5B and KMT5C, leading to epigenetic transcriptional repression. Controls histone H4 'Lys-20' trimethylation (PubMed:16612004).
Inhibits the intrinsic kinase activity of TAF1. Mediates transcriptional repression by SMARCA4/BRG1 by recruiting a histone deacetylase (HDAC) complex to the c-FOS promoter. In resting neurons, transcription of the c-FOS promoter is inhibited by BRG1-dependent recruitment of a phospho-RB1-HDAC1 repressor complex. Upon calcium influx, RB1 is dephosphorylated by calcineurin, which leads to release of the repressor complex (By similarity) (PubMed:15750587, PubMed:16612004, PubMed:8336704).
