May function as a transcriptional repressor. May also function as a ubiquitin ligase mediating ubiquitination of chromatin-associated TP53. Functions in cell survival and proliferation through control of the cell cycle. Functions in the p53 and pRB tumor suppressor pathways and regulates the cyclin CCNA2 transcription. S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. Protein modification; protein ubiquitination. Homodimer; binds DNA as a dimer (By similarity). Forms a complex with CDKN2A and TP53. Interacts with HDAC1, HMGA2 and RASSF1 (By similarity). Interactions with TP53, RB1, ANP32A and probably BMI1 and FHL2 regulate E4F1 activity. A small fraction is detected in the cytoplasm (By similarity). Excluded from the nucleolus where it is targeted upon CDKN2A overexpression. Localizes to the mitotic spindle during embryogenesis. Ubiquitously expressed. Continuously expressed during embryogenesis. Phosphorylated; phosphorylation is cell cycle-dependent and regulates DNA-binding activity and function. May be sumoylated by UBE2I upon interaction with CDKN2A. Death before 7.5 dpc probably at the peri-implantation stage. Blastocysts display defects in mitotic progression and chromosomal segregation and increased apoptosis.