title: Formation and morphology of dark puffs in Drosophila melanogaster polytene chromosomes.
abstract: The formation of unusual dark puffs in Drosophila melanogaster polytene chromosomes has been studied by electron microscopic (EM) analysis. Fly stocks transformed by the P[ry; Prat:bw] and P[hs-BRC-z1] constructs were used. In the former the bw gene is under the promoter of a housekeeping gene, Prat; in the latter the Br-C locus, mapping to the dark puff 2B, is under the promoter of a heat-shock gene, hsp70. Inserted into region 65A of the 3L chromosome, the Prat:bw copies give rise to structures which are morphologically reminiscent of the so-called "dark" puffs. In contrast, insertion of P[hs-BRC-z1] into region 99B of the 3R chromosome causes a regular "light" puff of form. Comparative analysis of the dark puffs--both transgenic and natural--suggests that there might be at least two mechanisms underlying their formation. One is a local incomplete decondensation of activated bands, characteristic of the so-called small puffs. The other is the formation of ectopic-looking contacts between the bands adjacent to the puffing zone. Transposition of the DNA, from which such a puff develops, causes a regular light puff to form at the new location. Heterochromatic regions do not appear to be directly involved in puffing.
authors.affiliation: Institute of Cytology and Genetics of the Siberian Branch of the Russian Academy of Sciences, Novosibirsk, 630090, Russia. semeshin@bionet.nsc.ru
authors.forename: V F
authors.initials: VF
authors.lastname: Semeshin
authors.forename: V V
authors.initials: VV
authors.lastname: Shloma
authors.forename: I F
authors.initials: IF
authors.lastname: Zhimulev
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D002871:Chromosome Banding; D002874:Chromosome Mapping; D002875:Chromosomes / Q000648:ultrastructure*; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000235:genetics* / Q000254:growth & development / Q000648:ultrastructure; D005786:Gene Expression Regulation; D017344:Genes, Insect; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics; D006570:Heterochromatin / Q000648:ultrastructure; D019476:Insect Proteins / Q000032:analysis; D007814:Larva; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D011401:Promoter Regions, Genetic; D012261:Ribonucleoproteins / Q000032:analysis; D014157:Transcription Factors / Q000235:genetics; D014158:Transcription, Genetic
chemical_list: C102117:Br protein, Drosophila; D029721:Drosophila Proteins; D018840:HSP70 Heat-Shock Proteins; D006570:Heterochromatin; D019476:Insect Proteins; D012261:Ribonucleoproteins; D014157:Transcription Factors