Editing Transcription factor (section)

=== Accessibility of DNA-binding site ===

In eukaryotes, DNA is organized with the help of [[histone]]s into compact particles called [[nucleosome]]s, where sequences of about 147 DNA base pairs make ~1.65 turns around histone protein octamers. DNA within nucleosomes is inaccessible to many transcription factors. Some transcription factors, so-called [[pioneer factor]]s are still able to bind their DNA binding sites on the nucleosomal DNA. For most other transcription factors, the nucleosome should be actively unwound by molecular motors such as [[Chromatin remodeling|chromatin remodelers]].<ref>{{Cite journal |vauthors=Teif VB, Rippe K |date=September 2009 |title=Predicting nucleosome positions on the DNA: combining intrinsic sequence preferences and remodeler activities |journal=Nucleic Acids Research |volume=37 |issue=17 |pages=5641–55 |doi=10.1093/nar/gkp610 |pmc=2761276 |pmid=19625488}}</ref> Alternatively, the nucleosome can be partially unwrapped by thermal fluctuations, allowing temporary access to the transcription factor binding site. In many cases, a transcription factor needs to [[Competitive inhibition|compete for binding]] to its DNA binding site with other transcription factors and histones or non-histone chromatin proteins.<ref>{{Cite journal |vauthors=Teif VB, Rippe K |date=October 2010 |title=Statistical-mechanical lattice models for protein-DNA binding in chromatin |journal=Journal of Physics: Condensed Matter |volume=22 |issue=41 |pages=414105 |arxiv=1004.5514 |bibcode=2010JPCM...22O4105T |doi=10.1088/0953-8984/22/41/414105 |pmid=21386588 |s2cid=103345}}</ref>  Pairs of transcription factors and other proteins can play antagonistic roles (activator versus repressor) in the regulation of the same [[gene]].{{cn|date=March 2024}}