[Structural features of chromatin organization of 3C6/C7 interband in Drosophila melanogaster polytene chromosomes]

This article presents an analysis of the causes of chromatin decompaction of interbands in Drosophila polytene chromosomes. On the example of interband 3C6/C7 of X chromosome, we investigate the ability of different DNA segments from the region to form an interband in a new genetic environment. Site-specific FLP recombination between two transposons with FRT-sites allows introducing the DNA fragments from the inter-band 3C6/C7 into plCon(dv) transposon located in cytologically well-characterized 84F region of chromosome 3 followed by electron microscopic analysis of changes in the region, caused by insertion of the DNA fragments into the transposon. Thus, it has shown that the insertion of DNA fragment 276 bp in length from 3C6/C7 region into the plCon(dv) transposon leads to the formation of a new interband between two thin bands which are represented by material of the transposon. To date, the DNA fragment is minimal known sequence that is necessary and sufficient for interband formation. In addition, the sequence containing three tandemly repeated copies of DNA fragment 0.9 kb including a fragment of 276 bp from the interband 3C6/C7 was integrated in the transposon. The presence of additional copies of the DNA fragment did not change the morphology of the resulting interband. It was shown that sites of hypersensitivity to DNase I persist in interbands formed in the new genetic environment. The data obtained allow us to start analysis of the specific factors (proteins, DNA motifs, etc.) that determine the formation of decompacted chromatin state in sertain interband region and, as a whole, chromometric organization of interphase chromosomes in Drosophila.