Genetic structure of the abd-A gene of Drosophila.

We report the embryonic and adult phenotypes of a number of mutations of the abd-A gene of the bithorax complex. Some of them result in loss of abd-A function in the whole abd-A domain and are usually lethal. These probably eliminate or inactivate abd-A protein products. Other mutations affect only part of the abd-A domain. These are viable, appear to map outside the abd-A transcription unit, and presumably alter the normal spatial regulation of abd-A products. We propose a model of abd-A structure based on a protein-coding region and two cis-regulatory regions. Regulatory region 1, 3' to the transcription unit, contains positive and negative regulatory elements. Regulatory region 2, 5' to the transcription unit, establishes the correct level of abd-A activity in the abdominal metameres.