Poster abstracts

Poster number 43 submitted by Yi Luo

Nucleosomes Accelerate Transcription Factor Dissociation

Yi Luo (Biophysics Graduate Program, The Ohio State University), Justin A. North (Department of Physics, The Ohio State University), Michael G. Poirier (Biophysics Graduate Program, Department of Physics and Department of Chemistry & Biochemistry, The Ohio State University)

Abstract:
Transcription factors (TF) bind DNA target sites within promoters to activate gene expression. TFs achieve high binding specificity on their recognition DNA sequence by binding with resident times of up to hours in vitro. However, in vivo TFs can exchange on the order of seconds. The factors that regulate TF dynamics in vivo and increase dissociation rates by orders of magnitude are not known. We investigated TF binding and dissociation dynamics at their recognition sequence within duplex DNA, single nucleosomes and short nucleosome arrays with single-molecule Total Internal Reflection Fluorescence (smTIRF) microscopy. We find that the rate of TF dissociation from its site within either nucleosomes or nucleosome arrays is increased by 1000-fold relative to duplex DNA. Our results suggest that TF binding within chromatin could be responsible for the dramatic increase in TF exchange in vivo. Furthermore, these studies demonstrate that nucleosomes regulate DNA-protein interactions not only by blocking DNA-protein binding but by dramatically increasing the dissociation rate of protein complexes from their DNA target sites.

Keywords: Nucleosome Dynamics, Transcription Factor, Single-molecule FRET