Editing Transcription factor (section)

== Number ==
{{main listing|List of human transcription factors|more=no}}
Transcription factors are essential for the regulation of gene expression and are, as a consequence, found in all living organisms. The number of transcription factors found within an organism increases with genome size, and larger genomes tend to have more transcription factors per gene.<ref name="pmid12957540">{{Cite journal |vauthors=van Nimwegen E |date=September 2003 |title=Scaling laws in the functional content of genomes |journal=Trends in Genetics |volume=19 |issue=9 |pages=479–84 |arxiv=physics/0307001 |doi=10.1016/S0168-9525(03)00203-8 |pmid=12957540 |s2cid=15887416}}</ref>

There are approximately 2800 proteins in the [[human genome]] that contain DNA-binding domains, and 1600 of these are presumed to function as transcription factors,<ref name="pmid15193307" /> though other studies indicate it to be a smaller number.<ref>{{Cite web |title=List Of All Transcription Factors In Human |url=https://www.biostars.org/p/53590/ |website=biostars.org}}</ref>  Therefore, approximately 10% of genes in the genome code for transcription factors, which makes this family the single largest family of human proteins.  Furthermore, genes are often flanked by several binding sites for distinct transcription factors, and efficient expression of each of these genes requires the cooperative action of several different transcription factors (see, for example, [[hepatocyte nuclear factors#Function|hepatocyte nuclear factors]]).  Hence, the combinatorial use of a subset of the approximately 2000 human transcription factors easily accounts for the unique regulation of each gene in the human genome during [[developmental biology|development]].<ref name="pmid11823631" />