Prior genetic studies have suggested a functional relationship between the product of the deltex gene and those of three of the so-called "neurogenic" loci, Notch, Delta and mastermind. To gain further insight into this relationship, we have proceeded with a molecular characterization of deltex. We report that deltex encodes a maternally and zygotically expressed transcript that conceptually translates to a basic protein of novel sequence. Immunolocalization of the protein reveals an apparently ubiquitous distribution in embryonic and imaginal tissues. Because our detection methods also reveal a very low level of protein accumulation within the cytoplasm of cells, we have used transgenic flies to confirm this observation by ectopically expressing deltex under the control of a heat shock gene promoter. The resulting overexpression rescues deltex mutant defects but does not produce any obvious phenotypic abnormalities in otherwise wild-type flies. Finally, we examine genetically several Supressor of deltex mutations for evidence of functional integration with deltex and other neurogenic genes. We demonstrate that in addition to suppressing all adult morphological defects of deltex alleles, these suppressors also are capable of suppressing most synergistic effects involving deltex and Notch, Delta and mastermind.