Transcription activator that binds DNA cooperatively with DP proteins through the E2 recognition site, 5'-TTTC[CG]CGC-3' found in the promoter region of a number of genes whose products are involved in cell cycle regulation or in DNA replication. The DRTF1/E2F complex functions in the control of cell-cycle progression from G1 to S phase. E2F1 binds preferentially RB1 in a cell-cycle dependent manner. It can mediate both cell proliferation and TP53/p53-dependent apoptosis. Blocks adipocyte differentiation by binding to specific promoters repressing CEBPA binding to its target gene promoters. Directly activates transcription of PEG10. Positively regulates transcription of RRP1B. BIRC2/c-IAP1 stimulates its transcriptional activity. Component of the DRTF1/E2F transcription factor complex. Forms heterodimers with DP family members. The E2F1 complex binds specifically hypophosphorylated retinoblastoma protein RB1. During the cell cycle, RB1 becomes phosphorylated in mid-to-late G1 phase, detaches from the DRTF1/E2F complex, rendering E2F transcriptionally active. Interacts with TRRAP, which probably mediates its interaction with histone acetyltransferase complexes, leading to transcription activation. Binds TOPBP1 and EAPP. Interacts with ARID3A. Interacts with TRIM28; the interaction inhibits E2F1 acetylation through recruiting HDAC1 and represses its transcriptional activity. Interaction with KAT2B; the interaction acetylates E2F1 enhancing its DNA-binding and transcriptional activity. Interacts with BIRC2/c-IAP1 (via BIR domains). The complex TFDP1:E2F1 interacts with CEBPA; the interaction prevents CEBPA binding to target genes promoters and represses its transcriptional activity. Interacts with RRP1B. Interacts with HCFC1. Interacts with KMT2E; the interaction is probably indirect and is mediated via HCFC1. Phosphorylated by CDK2 and cyclin A-CDK2 in the S-phase. Phosphorylation by CHEK2 stabilizes E2F1 upon DNA damage and regulates its effect on transcription and apoptosis. Phosphorylation at Ser-398 by GSK3B promotes interaction with USP11, leading to its deubiquitination and stabilization. Ubiquitinated via 'Lys-63'-linked ubiquitin, leading to its degradation. Deubiquitinated by USP11 follwong phosphorylation by GSK3B, promoting its stability. Acetylation stimulates DNA-binding. Enhanced under stress conditions such as DNA damage and inhibited by retinoblastoma protein RB1. Regulated by KAP1/TRIM28 which recruits HDAC1 to E2F1 resulting in deacetylation (By similarity). Belongs to the E2F/DP family.