Heterochromatin in Drosophila nasuta: restriction enzyme digestion of cytological preparations and genomic DNA

Abstract

In situ digestion of metaphase and polytene chromosomes and of interphase nuclei in different cell types of D. nausata with restriction enzymes revealed that enzymes like AluI, BeoRI, HaeIII, Sau3a and SinI did not affect Giemsa-stainability of heterochromatin while that of euchromatin was significantly reduced; TaqI and SalI digested both heterochromatin and euchromatin in mitotic chromosomes. Digestion of genomic DNA with AluI, EcoRI, HaeIII, Sau3a and KpnI left a >21kb DNA band undigested in agarose gels while with TaqI, no such undigested band was seen. The AluI-resistant >21kb DNA hybridized in situ specifically with the heterochromatic chromocentre. Purified. AT-rich satellite DNA of D. nasuta also hybridized in situ with heterochromatin regions while in southern hybridization, it hybridized specifically with the AluI-resistant >21kb DNA band. It is concluded that the satellite and other highly repetitive sequences present in the different heterochromatin blocks in karyotype of D. nasuta are remarkably homogeneous in their base sequence composition.