Downstream effector of Notch signaling. Transcriptional repressor which binds preferentially to the canonical E box sequence 5'-CACGTG-3'. Acts as a suppressor of neurogenesis by antagonizing proneural gene function. Functions during floorplate development. Plays a role in pronephros formation in the inhibition of distal tubule and duct cell fates and the promotion of glomus and proximal tubule formation. Efficient DNA binding requires dimerization with another bHLH protein. Binds DNA in the form of homodimer or more strongly as a heterodimer with hes1/hairy1 or hes4-B/hairy2b. Also weakly interacts with the bHLH proteins hes2, neurod1 and neurod4/ath3. Interacts (via Orange domain) with ccdc89/boip (via C-terminus). Expression in late gastrula and early neurula embryos is restricted to dorsal endodermal cells and the medial neural plate and in dorsal endodermal cells. Expression fills exactly the gap in between the two rows of motor neurons in the ventral neural tube. At later stages, expressed in the floor plate, in hypochord cells and in the somitogenic and anterior presomitic mesoderm. By tailbud stage, also highly expressed in the dorsal hindbrain, telencephalon and eye vesicles, olfactory placodes, branchial arches, tail fin and somites. Expression in the somite, eye, head and branchial arches persists throughout organogenesis. In addition, despite being absent in the early heart field, expression begins within the linear heart tube at stages 32-35. Also expressed from the early-tailbud stage in the dorsoanterior region of the developing pronephros. During early tailbud stages, localized to the most dorsoanterior portion of the pronephric anlagen. During late tailbud to early tadpole stages, expression marks the most dorsoanterior portion of the pronephros with expression becoming progressively restricted to the tip of the forming tubules. Pronephric expression is no longer detectable at late tadpole stages (stage 35). In adults, strongest expression is observed in the brain, eye, heart, lung, muscle, ovary, skin, spleen and testis. Expressed throughout embryogenesis, with expression rising after neurulation. By Notch signaling. The Orange domain, downstream sequence and the bHLH are required for efficient heterodimerization with hes/hairy proteins, and for transcriptional repressor activity. The C-terminal YRPW motif is not required for transcriptional repressor activity and is unable to recruit groucho. Belongs to the HEY family.