Identification and characterization of a parasegment specific regulatory element of the abdominal-B gene of Drosophila.

We have characterized mutations of the Abdominal-B gene of the bithorax complex of Drosophila. We conclude that the gene contains two distinct genetic elements: one has a morphogenetic role and acts in parasegments 10, 11, 12, and 13, while the other acts on parasegment 14 and has primarily or exclusively a regulatory function. Evidence indicates that the latter suppresses the activity of the morphogenetic element of Abd-B and of other genes responsible for the development of sclerotic plates. The regulatory element also suppresses those BX-C genes and other homeotics that, in the absence of Polycomb or extra sex combs function, can become active in parasegment 14.