Chromatin remodeling through directional DNA translocation from an internal nucleosomal site

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Abstract
The RSC chromatin remodeler contains Sth1, an ATP-dependent DNA translocase. On DNA substrates, RSC/Sth1 tracks along one strand of the duplex with a 3′ → 5′ polarity and a tracking requirement of one base, properties that may enable directional DNA translocation on nucleosomes. The binding of RSC or Sth1 elicits a DNase I–hypersensitive site approximately two DNA turns from the nucleosomal dyad, and the binding of Sth1 requires intact DNA at this location. Results with various nucleosome substrates suggest that RSC/Sth1 remains at a fixed position on the histone octamer and that Sth1 conducts directional DNA translocation from a location about two turns from the nucleosomal dyad, drawing in DNA from one side of the nucleosome and pumping it toward the other. These studies suggest that nucleosome mobilization involves directional DNA translocation initiating from a fixed internal site on the nucleosome.