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( Transcription factor)
In the field of molecular biology, a transcription factor (sometimes called a sequence-specific DNA binding factor) is a protein that binds to specific sequences of DNA and thereby controls the transfer (or transcription) of genetic information from DNA to RNA.[1][2] Transcription factors perform this function alone, or with other proteins in a complex, by promoting (as an activator), or blocking (as a repressor) the recruitment of RNA polymerase (the enzyme which activates the transcription of genetic information from DNA to RNA) to specific genes.[3][4][5] A defining feature of transcription factors is that they contain one or more DNA binding domains (DBDs) which attach to specific sequences of DNA adjacent to the genes that they regulate.[6][7] Additional proteins such as coactivators, chromatin remodelers, histone acetylases, deacetylases, kinases, and methylases, while also playing crucial roles in gene regulation, lack DNA binding domains, and therefore are not classified as transcription factors.[8] Transcription factors are essential for the regulation of gene expression and consequently are found in all living organisms. The number of transcription factors found within an organism increases with the genome size and the larger genomes tend to have more transcription factors per gene.[9] There are approximately 2600 proteins in the human genome that contain DNA-binding domains and most of these are presumed to function as transcription factors.[10] 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). 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 development.[8]
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