Genetic evidence suggests that E(spl), one of the neurogenic loci of Drosophila, is a gene complex comprising an as yet incompletely established number of transcription units. In order to correlate the various transcription units with E(spl) functions, wild-type flies were transformed with genomic DNA encoding the transcription unit m8 from the mutant E(spl)D, which was known to be altered in embryos carrying this mutant allele. Transformants show the same dominant enhancement of the spl phenotype as E(spl)D itself. Since m8 has a virtually identical pattern of expression as m4, m5 and m7, we have determined the sequence of these four transcripts. The deduced protein products of m5, m7 and m8 exhibit extensive sequence homology with each other. All three encode a sequence similar to one of the conserved domains of representatives of the vertebrate myc gene family which is also present in the deduced protein sequences of the Drosophila achaete-scute gene complex. Sequence analysis of the m8 transcription unit in the E(spl)D mutation revealed several DNA lesions. One of the lesions is a deletion in the region upstream of the transcription start site. Another lesion is a deletion in the coding region that leads to a shorter protein which, in addition, differs in its carboxy-terminal end from the wild-type protein by the presence of nine amino acids.