Transcription factor that binds to the E-box and functions as inhibitor of transcription. DNA binding requires dimerization with an E protein. Inhibits transcription activation by ASCL1/MASH1 by sequestering E proteins. Heterodimer with TCF3/E12. Interacts with the bHLH domain of TCF3/E12. Detected in the developing central nervous system, in particular in embryonic ventral neural tube, brain, and spinal cord. Detected in embryonic intestine. Detected in embryonic and adult thalamus, hypothalamus, midbrain, pons and medulla.