Cloning and characterization of a dispersed, multicopy, X chromosome sequence in Drosophila melanogaster.

We have isolated and characterized a dispersed middle repetitive DNA sequence from Drosophila melanogaster that is concentrated on the euchromatic portion of the X chromosome. In situ hybridization of the repeat unit to salivary gland chromosomes shows the sequence is distributed among approximately 10 major and 20 minor X chromosomal sites. Based on DNA sequence analysis of homologous sequences from three different cytogenetic regions, the 372-base-pair repeat unit appears to be (A + T)-rich and noncoding and shows strong sequence conservation among units from different chromosomal regions. The nature and distribution of this sequence are suggestive of the hypothetical X chromosome DNA sequences thought to be involved in the primary establishment of sex determination and dosage compensation in Drosophila.