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. E2F4 binds with high affinity to RBL1 and RBL2. In some instances can also bind RB1. Specifically required for multiciliate cell differentiation: together with MCIDAS and E2F5, binds and activate genes required for centriole biogenesis. Component of the DRTF1/E2F transcription factor complex. Binds cooperatively with TFDP1/Dp-1 to E2F sites. The E2F4/TFDP1 dimer interacts preferentially with pocket protein RBL1, which inhibits the E2F transactivation domain. Lower affinity interaction has been found with retinoblastoma protein RB1. Interacts with TRRAP, which probably mediates its interaction with histone acetyltransferase complexes, leading to transcription activation. Interacts with HCFC1. Component of the DREAM complex (also named LINC complex) at least composed of E2F4, E2F5, LIN9, LIN37, LIN52, LIN54, MYBL1, MYBL2, RBL1, RBL2, RBBP4, TFDP1 and TFDP2. The complex exists in quiescent cells where it represses cell cycle-dependent genes. It dissociates in S phase when LIN9, LIN37, LIN52 and LIN54 form a subcomplex that binds to MYBL2. Interacts with PML (isoform PML-1, isoform PML-2, isoform PML-3, isoform PML-4 and isoform PML-5). Interacts with CEBPA (when phosphorylated) (PubMed:15107404). Found in all tissue examined including heart, brain, placenta, lung, liver, skeletal muscle, kidney and pancreas. Present in the growth-arrested state, its abundance does not change significantly as cells move into and through the cell cycle. Differentially phosphorylated in vivo. The poly-Ser region of E2F4 is polymorphic and the number of Ser varies in the population (from 8 to 17). The variation might be associated with tumorigenesis. Belongs to the E2F/DP family.