β-Heterochromatin in drosophila: molecular organization and function. molecular biological analysis of a mar/sar dna sequence in centromeric heterochromatin of drosophila melanogaster

A molecular biological characteristic of a DNA fragment X20pl.4, which is a moderately repetitive sequence of the Drosophila melanogaster genome, is presented. The fragment is present in about 120 copies per haploid genome. The main pool of the A.20pl .4 homologous DNA can be isolated, along with the nuclear matrix DNA, and consists of Hind Nl-EcoR I monomers 1.4 - 1.6 kb in length. The monomers may occur in the genome as both single copies and tandem clusters forming chromosomes fragments up to 6 - 10 kb in length. The region of the ?i20pl.4 fragment between nucleotides 350 and 905 polymerizes with purified lamin from D. melanogaster. The sites of the fragment that had physical contact with lamin in vitro were determined using an Exo III protection. It was demonstrated that ATATTT, A, and T boxes located in four nonperfect tandem repeats were involved in the contact, both DNA strains reacting with lamin.