Discrete-length repeated sequences in eukaryotic genomes.

Two of the four repeated DNA sequences near the 5' end of the silk fibroin gene hybridize with discrete-length families of repeated DNA. These two families comprise 0.5% of the animal's genome. A repeated sequence with a conserved length has also been found in the short class of moderately repeated sequences in the sea urchin. The discrete length, interspersion, and sequence fidelity of these moderately repeated sequences suggests that each has been multiplied as a discrete unit. Thus, transposition mechanisms may be responsible for the multiplication and dispersion of a large class of repeated sequences in phylogenetically diverse eukaryotic genomes. The repeat we have studied in most detail differs from previously described eukaryotic transposable elements: it is much shorter (1300 base pairs) and does not have terminal repetitions detectable by DNA hybridization. A simple technique for identifying such discrete-length repeated sequences is described.