Sequences of the 1.672 g/cm3 satellite DNA of Drosophila melanogaster.

The 1.672 g/cm³ satellite DNA of Drosophila melanogaster was purified by successive equilibrium centrifugations in a CsCl gradient, an actinomycin $\text{D}\text{CsCl}$ gradient, and a netropsin sulfate/CsCl gradient. The resulting DNA was homogeneous by the physical criteria of thermal denaturation, renaturation kinetics and equilibrium banding in each of the gradients listed above. In addition, the complementary strands could be separated in an alkaline CsCl gradient. Despite this rigorous purification procedure, nucleotide sequence analysis indicates the presence of two different DNA species in this satellite, poly $\text{A-A-T-A-T}\text{T-T-A-T-A}$ and poly$\text{A-A-T-A-T-A-T}\text{T-T-A-T-A-T-A}$. Further physical, chemical and template properties of the isolated complementary strands demonstrate that these two repeating sequences are not interspersed with each other. This result has biological significance since sequences of this particular satellite are known to be located primarily on two different chromosomes, Y and 2. These results further suggest that the sequence heterogeneity observed in satellite DNA of higher eukaryotes may result from mixtures of very closely related but molecularly homogeneous repeated sequences each restricted to a particular chromosome or chromosomal region.