title: Cis and trans interactions between the iab regulatory regions and abdominal-A and abdominal-B in Drosophila melanogaster.
abstract: The infra-abdominal (iab) elements in the bithorax complex of Drosophila melanogaster regulate the transcription of the homeotic genes abdominal-A (abd-A) and Abdominal-B (Abd-B) in cis. Here we describe two unusual aspects of regulation by the iab elements, revealed by an analysis of an unexpected complementation between mutations in the Abd-B transcription unit and these regulatory regions. First, we find that iab-6 and iab-7 can regulate Abd-B in trans. This iab trans regulation is insensitive to chromosomal rearrangements that disrupt transvection effects at the nearby Ubx locus. In addition, we show that a transposed Abd-B transcription unit and promoter on the Y chromosome can be activated by iab elements located on the third chromosome. These results suggest that the iab regions can regulate their target promoter located at a distant site in the genome in a manner that is much less dependent on homologue pairing than other transvection effects. The iab regulatory regions may have a very strong affinity for the target promoter, allowing them to interact with each other despite the inhibitory effects of chromosomal rearrangements. Second, by generating abd-A mutations on rearrangement chromosomes that break in the iab-7 region, we show that these breaks induce the iab elements to switch their target promoter from Abd-B to abd-A. These two unusual aspects of iab regulation are related by the iab-7 breakpoint chromosomes that prevent iab elements from acting on Abd-B and allow them to act on abd-A. We propose that the iab-7 breaks prevent both iab trans regulation and target specificity by disrupting a mechanism that targets the iab regions to the Abd-B promoter.
authors.affiliation: Department of Human Genetics, Howard Hughes Medical Institute, University of Utah, Salt Lake City 84112, USA.
authors.forename: J E
authors.initials: JE
authors.lastname: Hendrickson
authors.forename: S
authors.initials: S
authors.lastname: Sakonju
mesh_terms: D000818:Animals; D004268:DNA-Binding Proteins / Q000235:genetics; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000196:embryology / Q000235:genetics*; D004742:Enhancer Elements, Genetic / Q000235:genetics; D005260:Female; D018507:Gene Expression Regulation, Developmental / Q000235:genetics*; D015321:Gene Rearrangement; D005801:Genes, Homeobox / Q000235:genetics; D017344:Genes, Insect / Q000235:genetics; D005816:Genetic Complementation Test; D018398:Homeodomain Proteins; D007301:Insect Hormones / Q000235:genetics*; D008297:Male; D009154:Mutation / Q000502:physiology; D009687:Nuclear Proteins; D011401:Promoter Regions, Genetic / Q000235:genetics; D011506:Proteins / Q000235:genetics*; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics*; D013909:Thorax / Q000254:growth & development; D014157:Transcription Factors; D014178:Translocation, Genetic; D014998:Y Chromosome
chemical_list: C062393:Abd-B proteins, Drosophila; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D007301:Insect Hormones; D009687:Nuclear Proteins; D011506:Proteins; D014157:Transcription Factors; C066177:Ubx protein, Drosophila; C066591:abd-A protein, Drosophila