Polymer reptation and nucleosome repositioning

We consider how beads can diffuse along a chain that wraps them, without be coming displaced from the chain: our proposed mechanism is analogous to the reptation of "stored length" in more familiar situations of polymer dynami cs. The problem arises in the case of globular aggregates of proteins (hist ones) that are wound by DNA in the chromosomes of plants and animals; these beads (nucleosomes) are multiply wrapped and yet are able to reposition th emselves over long distances, while remaining bound hv the DNA chain.