title: The heterochromatin-associated protein HP-1 is an essential protein in Drosophila with dosage-dependent effects on position-effect variegation.
abstract: Chromosome rearrangements which place euchromatic genes adjacent to a heterochromatic breakpoint frequently result in gene repression (position-effect variegation). This repression is thought to reflect the spreading of a heterochromatic structure into neighboring euchromatin. Two allelic dominant suppressors of position-effect variegation were found to contain mutations within the gene encoding the heterochromatin-specific chromosomal protein HP-1. The site of mutation for each allele is given: one converts Lys169 into a nonsense (ochre) codon, while the other is a frameshift after Ser10. In flies heterozygous for one of the mutant alleles (Su(var)2-504), a truncated HP-1 protein was detectable by Western blot analysis. An HP-1 minigene, consisting of HP-1 cDNA under the control of an Hsp70 heat-inducible promoter, was transduced into flies by P element-mediated germ line transformation. Heat-shock driven expression of this minigene results in elevated HP-1 protein level and enhancement of position-effect variegation. Levels of variegating gene expression thus appear to depend upon the level of expression of a heterochromatin-specific protein. The implications of these observations for mechanism of heterochromatic position effects and heterochromatin function are discussed.
authors.affiliation: Edward A. Doisy Department of Biochemistry and Molecular Biology, St. Louis University School of Medicine, Missouri 63104.
authors.forename: J C
authors.initials: JC
authors.lastname: Eissenberg
authors.forename: G D
authors.initials: GD
authors.lastname: Morris
authors.forename: G
authors.initials: G
authors.lastname: Reuter
authors.forename: T
authors.initials: T
authors.lastname: Hartnett
mesh_terms: D000483:Alleles; D000818:Animals; D000090266:Chromobox Protein Homolog 5; D002868:Chromosomal Proteins, Non-Histone / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D004247:DNA / Q000235:genetics; D004331:Drosophila melanogaster / Q000235:genetics / Q000502:physiology*; D004843:Epistasis, Genetic; D005786:Gene Expression Regulation; D005804:Genes, Lethal; D016153:Genes, Suppressor; D006570:Heterochromatin / Q000502:physiology; D009154:Mutation; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis
chemical_list: D002868:Chromosomal Proteins, Non-Histone; D006570:Heterochromatin; D011993:Recombinant Fusion Proteins; D000090266:Chromobox Protein Homolog 5; D004247:DNA