Regulation of the Ultrabithorax gene of Drosophila by other bithorax complex genes.

The bithorax complex of Drosophila is composed of three major units of gene function, Ultrabithorax (Ubx), abdominal-A (abd-A), and Abdominal-B (Abd-B), each having a precise realm of action within the thorax and abdomen. Recent molecular studies have established that the transcripts and protein products of the Ubx gene are expressed principally in a restricted portion of the body, beginning in the second thoracic segment and ending in the eighth abdominal segment (i.e., in parasegments 5-13). However, within this region, both show complex, heterogeneous patterns of expression. Using mutations in the abd-A, Abd-B, and esc (extra sex combs) genes we show that these distinct patterns result in large part from regulation of Ubx gene expression by the abd-A and Abd-B gene functions.