NESTED RETROTRANSPOSONS IN THE INTERGENIC REGIONS OF THE MAIZE GENOME

The relative organization of genes and repetitive DNAs in complex euka ryotic genomes is not well understood. Diagnostic sequencing indicated that a 280-kilobase region containing the maize Adh1-F and u22 genes is composed primarily of retrotransposons inserted within each other. Ten retroelement families were discovered, with reiteration frequencie s ranging from 10 to 30,000 copies per haploid genome, These retrotran sposons accounted for more than 60 percent of the Adh1-F region and at least 50 percent of the nuclear DNA of maize. These elements were lar gely intact and are dispersed throughout the gene-containing regions o f the maize genome.