The heterochromatin of Drosophila, as of other eukaryotes, accounts for a substantial fraction of the genome, but its organization and function is little understood. Rex (Ribosomal exchange) is one of very few heterochromatic loci that have been identified, and its analysis will provide a significant increase in our understanding of heterochromatin. This locus is a maternal-effect dominant located in the basal heterochromatin of the X chromosome that promotes recombination of the ribosomal RNA genes during early mitotic divisions in offspring of Rex females. Molecular and genetic analysis of Rex and of Rex-generated recombinants will focus on dissecting Rex, and on understanding the mechanism by which it induces rDNA exchange. This project will increase our understanding of the heterochromatic regions of chromosomes. Heterochromatin has been difficult to analyze in the past. This project uses unique methods not found elsewhere. An understanding of heterochromatin in fruit flies will be readily transferable in principle to the large fraction of heterochromatin found in all mammals including man.
