title: Beta-cell differentiation factor Nkx6.1 contains distinct DNA binding interference and transcriptional repression domains.
abstract: beta-Cell differentiation factor Nkx6.1 is a homeodomain protein expressed in developing and mature beta-cells in the pancreatic islets of Langerhans. To understand how it contributes to beta-cell development and function, we characterized its DNA binding and transactivation properties. A single copy of the homeodomain of Nkx6. 1 binds to a strictly conserved 8-base pair DNA consensus sequence, TTAATTAC; even minor variations to this consensus reduce DNA binding affinity significantly. Full-length Nkx6.1, however, has markedly reduced DNA binding affinity due to an acidic domain at the carboxyl end of the molecule that functions as a mobile binding interference domain capable of interrupting the interaction between DNA and DNA binding domains of the helix-turn-helix type. When expressed in fibroblast cell lines, Nkx6.1 represses transcription through isolated Nkx6.1 binding sites; in beta-cell lines, Nkx6.1 specifically represses the intact insulin promoter through TAAT-containing sequences. In Gal4 one-hybrid fusion studies, transcriptional repression maps to a discreet region within the amino terminus. Our findings suggest a model in which Nkx6.1, regulated by interactions through its carboxyl terminus, directs the repression of specific genes in developing and mature beta-cells.
authors.affiliation: Hormone Research Institute and Department of Medicine, University of California, San Francisco, California 94143, USA.
authors.forename: R G
authors.initials: RG
authors.lastname: Mirmira
authors.forename: H
authors.initials: H
authors.lastname: Watada
authors.forename: M S
authors.initials: MS
authors.lastname: German
mesh_terms: D016475:3T3 Cells; D000818:Animals; D001483:Base Sequence; D002454:Cell Differentiation / Q000502:physiology*; D006224:Cricetinae; D004247:DNA / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D007328:Insulin / Q000235:genetics; D007515:Islets of Langerhans / Q000166:cytology*; D051379:Mice; D016296:Mutagenesis; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D014158:Transcription, Genetic
chemical_list: D018398:Homeodomain Proteins; D007328:Insulin; C491328:Nkx6-1 protein, mouse; D004247:DNA