[Formation of interdisks from the P-element DNA material in Drosophila polytene chromosomes]

Electron microscopical (EM) analysis of regions of Drosophila melanogaster polytene chromosomes containing a matrial of the P element was carried out. In one of the stocks analysed the DNA fragment of 54 kb in length was inserted in the genome by the P element-mediated transformation. This fragment consists of four tandemly repeated copies of the rosy gene and each of them has P-DNAs at the terminal sites. In polytene chromosomes the fragment forms a complex of loose chromatin, where, nevertheless, it is possible to distinguish four bands. EM analysis of two regions with the P element in other stock reveals lengthening of interbands, as compared with the same interbands in the initial stock without the P element. In the third of the stocks analysed the P element was inserted in the region of vermilion gene which is situated in the large single band, 10A1-2 of the X-chromosome. In this case, the splitting of the band into two unequal parts and formation of a new interband was observed. Data obtained show the possibility of interband formation from DNA material of the P element, which is probably connected with its transcriptional activity.