Formation and morphology of dark puffs in Drosophila melanogaster polytene chromosomes.
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.
Semeshin
V F
VF
Institute of Cytology and Genetics of the Siberian Branch of the Russian Academy of Sciences, Novosibirsk, 630090, Russia. semeshin@bionet.nsc.ru
Shloma
V V
VV
Zhimulev
I F
IF
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
C102117:Br protein, Drosophila; D029721:Drosophila Proteins; D018840:HSP70 Heat-Shock Proteins; D006570:Heterochromatin; D019476:Insect Proteins; D012261:Ribonucleoproteins; D014157:Transcription Factors