Internal organization of long repetitive DNA sequences in sea urchin genomes.

Abstract

Reassociated long repeat DNA from sea urchins [Lytechnius variegatus, L. pictus and Sphaerechinus granularis] is thermostable, indicating the absence of evolutionarily diverged families of repeated sequences. When fragments of radiolabeled long repeat DNA were denatured and reassociated with intact long repeat driver DNA, then sheared to 350 basepairs and assayed for thermal stability, the level of mismatch found in the duplexes varied inversely with the length of the starting fragments. This effect was due directly to the physical size of the molecules involved in reassociation. These results are consistent with and support a model for long repeat DNA in which short units of repetition are arranged in precise arrays. The significance of this arrangement of sequence units within long repeat DNA is discussed.