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PLoS One. 2014 Oct 21;9(10):e108575. doi: 10.1371/journal.pone.0108575. eCollection 2014.

An integrated model of transcription factor diffusion shows the importance of intersegmental transfer and quaternary protein structure for target site finding.

Author information

1
Department of Biochemistry & Cambridge Systems Biology Centre, University of Cambridge, Cambridge, United Kingdom.
2
Department of Biochemistry & Cambridge Systems Biology Centre, University of Cambridge, Cambridge, United Kingdom; Nuclear Dynamics Programme, The Babraham Institute, Cambridge, United Kingdom.
3
Fred Hutchinson Cancer Research Center, Seattle, Washington, United States of America.

Abstract

We present a computational model of transcription factor motion that explains both the observed rapid target finding of transcription factors, and how this motion influences protein and genome structure. Using the Smoldyn software, we modelled transcription factor motion arising from a combination of unrestricted 3D diffusion in the nucleoplasm, sliding along the DNA filament, and transferring directly between filament sections by intersegmental transfer. This presents a fine-grain picture of the way in which transcription factors find their targets two orders of magnitude faster than 3D diffusion alone allows. Eukaryotic genomes contain sections of nucleosome free regions (NFRs) around the promoters; our model shows that the presence and size of these NFRs can be explained as their acting as antennas on which transcription factors slide to reach their targets. Additionally, our model shows that intersegmental transfer may have shaped the quaternary structure of transcription factors: sequence specific DNA binding proteins are unusually enriched in dimers and tetramers, perhaps because these allow intersegmental transfer, which accelerates target site finding. Finally, our model shows that a 'hopping' motion can emerge from 3D diffusion on small scales. This explains the apparently long sliding lengths that have been observed for some DNA binding proteins observed in vitro. Together, these results suggest that transcription factor diffusion dynamics help drive the evolution of protein and genome structure.

PMID:
25333780
PMCID:
PMC4204827
DOI:
10.1371/journal.pone.0108575
[Indexed for MEDLINE]
Free PMC Article

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