The homeotic genes in Drosophila are aligned on the chromosome in the order of the body segments that they affect. The genes affecting the more posterior segments repress the more anterior genes. This posterior dominance rule must be qualified in the case of abdominal-A (abd-A) repression by Abdominal-B (Abd-B).Animals lacking Abd-B show ectopic expression of abd-A in the epidermis of the eighth abdominal segment, but not in the central nervous system. Repression in these neuronal cells is accomplished by a 92 kb noncoding RNA. This "iab-8 RNA" accomplishes the repression of abd-A by two redundant mechanisms; one, through the generation of a microRNA from the iab 3 regulatory region, to limit the ABD-A protein levels and a second mechanism that requires transcription in "cis" to abd-A promoter, which lies just downstream of the iab-8 RNA poly(A) site. Based on the cis-dependency, transcriptional interference with the abd-A promoter is the most likely second mechanism.