YRPW motif. Hey1 and Hey2 show identical domain organization, whereas HeyL lacks the full KPYRPWG motif, which resembles the characteristic carboxy-terminal WRPW motif of hairy/Enhancer-of-split and Hes proteins. The conserved terminal TEIGAF motif present in all three mammalian Hey proteins has not been found in other protein sequences before, and its significance is unclear. In the amino-terminal half, the basic domain immediately precedes the helix-loop-helix domain, which is in turn followed by the orange domain. The latter is capable of forming two additional helices.