Interacts with RB1 and EP300 and acts as a repressor of MYOD1 transactivation. Inhibits EP300 and CBP histone acetyltransferase activity. May be involved in coupling cell cycle exit to the transcriptional activation of genes required for cellular differentiation. May act as a candidate coinhibitory factor for NR0B2 that can be directly linked to transcription inhibitory mechanisms. Interacts via its LXCXE motif with the entire pocket region of RB1. Interacts with EP300, NR0B2 and TRIM27. May shuttle between nucleus and cytoplasm. Widely expressed. Most abundantly expressed in heart, skeletal muscle, pancreas, brain and testis. Expressed at much lower levels in placenta and peripheral blood leukocyte. Barely detectable in lung. Also weakly expressed in lung carcinoma A-549 and various leukemia cell lines. Expression decreased with development in ventricular tissue while remaining highly expressed in adult atrial tissue. In primary cultures of human skeletal myocytes, expression decreased during myogenic differentiation (at protein level). Down-regulated in differentiating U-937 leukemia cells. Ubiquitinated in U2OS osteosarcoma cells and is rapidly degraded by proteasome as cells exit the cell cycle exit. Inhibition of MYOD1 may be partly due to the ability of EID1 to bind and inhibit EP300 histone acetyltransferase activity.