title: ATP-dependent looping of DNA by ISWI.
abstract: Snf2 related chromatin remodelling enzymes possess an ATPase subunit similar to that of the SF-II helicases which hydrolyzes ATP to track along DNA. Translocation and any resulting torque in the DNA could drive chromatin remodeling. To determine whether the ISWI protein can translocate and generate torque, tethered particle motion experiments and atomic force microscopy have been performed using recombinant ISWI expressed in E. coli. In the absence of ATP, ISWI bound to and wrapped DNA thereby shortening the overall contour length measured in atomic force micrographs. Although naked DNA only weakly stimulates ATP hydrolysis by ISWI, both atomic force microscopy and tethered particle motion data indicate that the protein generated loops in the presence of ATP. The duration of the looped state of the DNA measured using tethered particle motion was ATP-dependent. Finally, ISWI relaxed positively supercoiled plasmids visualized by atomic force microscopy. While other chromatin remodeling ATPases catalyze either DNA wrapping or looping, both are catalyzed by ISWI.
authors.affiliation: Harvard University, Chemistry & Chemical Biology Dept., Cambridge, MA, USA.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Lia
authors.forename: Marco
authors.initials: M
authors.lastname: Indrieri
authors.forename: Tom
authors.initials: T
authors.lastname: Owen-Hughes
authors.forename: Laura
authors.initials: L
authors.lastname: Finzi
authors.forename: Alessandro
authors.initials: A
authors.lastname: Podesta
authors.forename: Paolo
authors.initials: P
authors.lastname: Milani
authors.forename: David
authors.initials: D
authors.lastname: Dunlap