The Enhancer of split [E(spl)] locus of Drosophila encodes seven independent helix-loop-helix proteins.

The E(spl) locus is thought to participate in a cell interaction mechanism that controls the choice of many cell fates during Drosophila development, including the segregation of neural precursors. Previous studies have demonstrated that E(spl) is defined by two groups of closely related transcripts, (i) a cluster of three transcripts encoding proteins bearing a helix-loop-helix (HLH) motif and (ii) a single-copy gene encoding a nuclear protein containing repeated motifs first identified in the beta subunit of guanine nucleotide-binding proteins. Both groups interact genetically with the Notch locus, which codes for a transmembrane protein. We report the structure of four additional HLH-encoding genes that reside in the E(spl) complex and provide evidence that we have now identified all the remaining members of the E(spl) HLH cluster.