title: Enhancer sequences influence the role of the amino-terminal domain of bicoid in transcription.
abstract: Bicoid (Bcd) is a Drosophila melanogaster morphogenetic gradient that controls embryonic patterning by activating target gene expression in a concentration-dependent manner. In this study we describe experiments to determine how different enhancers respond to Bcd distinctively, focusing on two natural Bcd-responsive enhancer elements, hunchback (hb) and knirps (kni). Our results show that, on the hb enhancer element, the amino-terminal domain of Bcd (residues 1 to 91) plays primarily an inhibitory role, whereas on the kni enhancer element this same Bcd domain plays a positive role at low protein concentrations. We further demonstrate that while the amino-terminal domain is largely dispensable for cooperative binding to the hb enhancer element, it is preferentially required for cooperative binding to the kni enhancer element. Alteration of the arrangement of Bcd binding sites in the kni enhancer element reduces the role of the amino-terminal domain in cooperative DNA binding but increases the effectiveness of the self-inhibitory function. In addition, elimination of symmetric pairs of Bcd binding sites in the kni enhancer element reduces both DNA binding and activation by Bcd. We propose that the amino-terminal domain of Bcd is an enhancer-specific switch that contributes to the protein's ability to activate different target genes in distinct manners.
authors.affiliation: Graduate Program in Molecular and Developmental Biology, Division of Developmental Biology, Children's Hospital Research Foundation, University of Cincinnati College of Medicine, Cincinnati, Ohio 45229, USA.
authors.forename: Dechen
authors.initials: D
authors.lastname: Fu
authors.forename: Chen
authors.initials: C
authors.lastname: Zhao
authors.forename: Jun
authors.initials: J
authors.lastname: Ma
mesh_terms: D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D015500:Chloramphenicol O-Acetyltransferase / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004330:Drosophila; D029721:Drosophila Proteins; D004742:Enhancer Elements, Genetic; D018398:Homeodomain Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D010957:Plasmids / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D015534:Trans-Activators / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D015534:Trans-Activators; C056478:bcd protein, Drosophila; D004247:DNA; D015500:Chloramphenicol O-Acetyltransferase; D001616:beta-Galactosidase