Identification and molecular genetic characterization of the polytene chromosome interbands in Drosophila melanogaster

Abstract

Being inserted into the polytene chromosome interbands, P transposable elements integrated in the genome of Drosophila produce new bands, enabling their use as markers of interband positions on the physical map. Molecular genetic analysis of 13 interbands marked as described showed that in most cases these regions were represented by intergenic spacers and by 5' noncoding regions of the genes. The interband regions consist of unique chromatin type whose decondensation is not obviously associated with transcription. In addition, interbands are enriched with the specific CHRIZ protein. Comparison of chromosomal protein sets and histone modifications in the polytene chromosome interband regions and in the corresponding sequences of the diploid cell chromosomes demonstrated their complete similarity relative these characteristics. In both cell types, interband regions contained open chromatin markers, including RNA polymerase II, ORC, GAF, TRX, and acetylated histones. At the same time, these regions appeared to be depleted of the repressed chromatin proteins, PC, E(Z), H3K9Me3, H3K27Me3, and some others. The similarity between interband chromosomal regions from different cell types is also manifested in the sets of DNAse I hypersensitive sites, which proved to be hot spots for transposon insertions. Our results suggest that band-interband structure is a fundamental principle of the interphase chromosome organization.