Hey genes (Hey1, Hey2 and HeyL) encode a new group of basic helix-loop-helix transcription factors that are related to the hairy/Enhancer of split genes. In the present study, we cloned and characterized the promoter region of the human and mouse Hey1 gene. The transcription initiation site was located 138 nucleotides upstream of the start codon. There is a minimal sequence element (nt -30 to -247) that is essential and important for basal transcription in three different cell types. Further upstream, a highly conserved sequence block (nt -324 to -646; approximately 90% human/mouse similarity) could be identified that contains several putative binding sites for transcription factors and likely represents an important regulatory region for this gene. Cotransfection experiments demonstrated that the mHey1 promoter activity is up-regulated by the activated form of all four mammalian Notch receptors via two functional RBP-Jkappa binding sites. The other members of the Hey gene family, Hey2 and HeyL, also possess RBP-Jkappa binding sites and they are similarly responsive to Notch signaling. Thus, our data clearly demonstrate that Hey genes form a new class of Notch signal transducers that should prove to be relevant in various developmental processes.