The correct segregation of neural from epidermal lineages in Drosophila embryogenesis depends on the activity of the six zygotic "neurogenic" genes. One of the neurogenic genes, Enhancer of split, is particularly noteworthy in its genetic interactions with Notch and Delta, which both appear to code for transmembrane proteins with homology to the epidermal growth factor. Transformation experiments have demonstrated the cloning of sequences necessary for Enhancer of split gene function. We report here that the gene product derived from DNA sequencing shows homology to the beta subunit of mammalian G proteins and CDC4, a yeast cell cycle gene. We demonstrate that expression of the transcripts relates to the developing central nervous system. These data suggest a mechanism of interaction between the gene products of Notch and Enhancer of split.