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Brutlag, D.L. (1977). In The Molecular Biology of the Mammalian Genetic Apparatus, New York: North-Holland Publishing. pp. 43-50.

The highly repeated DNA sequences of Drosophila melanogaster.

D. Brutlag

The highly repeated DNA sequences of eukaryotes can usually be isolated as satellites in CsCI buoyant gradients. The tandem arrangement of short repeated sequences gives rise to the distinctive physical properties of satellites. These DNAs are usually restricted to centromeric heterochromatin and, as might be expected, are neither transcribed nor translated. The function of centric heterochromatin is difficult to assess because, like satellite DNA itself, it is so variable between closely related species. Centric heterochromatin in Drosophila was thought to be genetically inert due to the lack of genes in this region and the viability of large heterochromatic deletions. However, such deletions in the sex chromosomes do result in improper disjunction in the first meiotic division and cause a marked decrease in fertility. This genetic evidence indicates that centric heterochromatin and perhaps satellite DNAs are involved in normal chromosome propagation in meiosis. We have, therefore, been studying the arrangement of satellite DNA in the heterochromatin in Drosophila in order to provide a molecular basis for such a proposed function.

We have found that the bulk of the heterochromatic DNA of Drosophila consists of four different satellite species. These DNAs contain short nucleotide sequences tandemly repeated in arrays over 1,000,000 base pairs long. Several of these satellites. although appearing homogeneous by many physical criteria, contain more than one distinct DNA with different repeating sequences, The sequences in one satellite are so similar that the different DNAs cannot be separated by classical procedures. I will conclude this paper by summarizing the progress we have made in separating these components by cloning individual molecules in hybrid bacterial plasmids.

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