Direct measurement of local chromatin fluidity using optical trap modulation force spectroscopy.
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.
Roopa
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Raman Research Institute, Bangalore, India.
Shivashankar
G V
GV
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
D002843:Chromatin; D006657:Histones