Binds to the E-box consensus sequence 5'-CANNTG-3' as a heterodimer and inhibits transcriptional activation by MYOD1, MYOG, MEF2A and MEF2C. Also represses expression of pro-inflammatory cytokines such as TNFA and IL1B. Involved in postnatal glycogen storage and energy metabolism. Inhibits the premature or ectopic differentiation of preosteoblast cells during osteogenesis, possibly by changing the internal signal transduction response of osteoblasts to external growth factors (By similarity). Efficient DNA binding requires dimerization with another bHLH protein. Forms a heterodimer with TCF3/E12. Also interacts with MEF2C. Mainly nuclear during embryonic development. Cytoplasmic in adult tissues. Expressed at low levels in sclerotome and dermatome of somites, and in limb buds at 10.5 dpc. Accumulates predominantly in dermatome, prevertebrae and derivatives of branchial arches by 13 dpc. Also expressed near surface of embryo and in chondrogenic cells. In adult, expressed at low levels in skin, bladder, uterus, aorta and heart. In the embryo, expression is detected at 10.5 dpc, increases continuously through to 17.5 dpc and is also high in neonates. Down-regulated in adults. By TNF-alpha. The C-terminal and HLH domains are essential for transcriptional repression.