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 (By similarity). 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/hairy2b. Also weakly interacts with the bHLH proteins hes2, neurod1 and neurod4/ath3. Interacts (via Orange domain) with ccdc89/boip (via C-terminus) (By similarity). 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.