encodes a member of the hairy and enhancer of split-related (HESR) family of basic helix-loop-helix (bHLH)-type transcription factors. The sequence of the encoded protein contains a conserved bHLH and orange domain, but its YRPW motif has diverged from other HESR family members. It is thought to be an effector of Notch signaling and a regulator of cell fate decisions. Alternatively spliced transcript variants have been found, but their biological validity has not been determined.The deduced 328-amino acid protein contains the basic helix-loop-helix and orange domains conserved in HEY proteins, but it lacks the YRPW motif found in HEY1 and HEY2. HEYL shares 78% amino acid identity with the mouse protein, with most divergence in the C-terminal domain.