CONSERVATION OF BROWN GENE TRANS-INACTIVATION IN DROSOPHILA

The mechanism underlying trans-inactivation associated with dominant p osition effect variegation (PEV) of the Drosophila melanogaster brown gene has been addressed by a comparison with its D. virilis homologue. This comparison revealed: 86% identity between conceptual translation products of the brown gene from these two species, functional homolog y, as the D. virilis gene rescues a D. melanogaster null brown mutatio n, and conservation of the sequences required for trans-inactivation, as the D. virilis gene in D. melanogaster is subject to dominant PEV. An extended region of sequence similarity upstream of the open reading frame is observed. As the D. virilis homologue is functionally interc hangeable with the D. melanogaster gene, these genes must share regula tory sequences as well as protein coding homology. These results suppo rt a model in which trans-inactivation is mediated by a heterochromati n-sensitive transcription factor.