title: Direct measurement of local chromatin fluidity using optical trap modulation force spectroscopy.
abstract: Chromatin assembly is condensed by histone tail-tail interactions and other nuclear proteins into a highly compact structure. Using an optical trap modulation force spectroscopy, we probe the effect of tail interactions on local chromatin fluidity. Chromatin fibers, purified from mammalian cells, are tethered between a microscope coverslip and a glass micropipette. Mechanical unzipping of tail interactions, using the micropipette, lead to the enhancement of local fluidity. This is measured using an intensity-modulated optically trapped bead positioned as a force sensor on the chromatin fiber. Enzymatic digestion of the histone tail interactions of tethered chromatin fiber also leads to a similar increase in fluidity. Our experiments show that an initial increase in the local fluidity precedes chromatin decompaction, suggesting possible mechanisms by which chromatin-remodeling machines access regulatory sites.
authors.affiliation: Raman Research Institute, Bangalore, India.
authors.forename: T
authors.initials: T
authors.lastname: Roopa
authors.forename: G V
authors.initials: GV
authors.lastname: Shivashankar
mesh_terms: D002843:Chromatin / Q000737:chemistry* / Q000302:isolation & purification; D006367:HeLa Cells; D006657:Histones / Q000737:chemistry*; D006801:Humans; D052898:Optical Tweezers; D013057:Spectrum Analysis; D013314:Stress, Mechanical; D014783:Viscosity
chemical_list: D002843:Chromatin; D006657:Histones