Abstract
Two nuclear DNA fractions from Drosophila hydei were isolated by silver ion and actinomycin D binding and centrifugation in isopycnic salt gradients. Neither fraction is composed of nor does it contain any highly repetitive simple sequence DNA, as shown by melting and reassociation studies. — One fraction has a CsCl density of 1.702 g/cm3 and hybridizes in situ with the β-heterochromatin of the chromocenter in polytene cells. This DNA fraction was found to be replicated during polytenization. In diploid cells this 1.702 g/cm3 component hybridizes to the heterochromatin of all four large autosome pairs, the middle part of the long arm of the Y-chromosome, but not to the X-heterochromatin. — A second fraction has a CsCl density of 1.697 g/cm3 and hybridizes in situ with polytene cells to the chromocenter and the nucleolus, but on metaphase chromosomes only to the nucleolus organizer regions.
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