Transcription factor

Transcription factors are proteins that bind to specific DNA sequences in order to regulate gene expression. They can act as activators or repressors, respectively increasing or decreasing the transcription of a target gene. Some transcription factors function by directly recruiting (or, conversely, blocking the recruitment of) RNA polymerase to the promoter region of a target gene; however, the majority of transcription factors function through interaction with one or more adapter proteins.

Transcription factors comprise several protein families (groups of closely related proteins), many of which are found in every lineage of organism. Genes encoding for transcription factors make up a significant portion of every organism's genome. There are estimated to be well over 2000 genes (some estimates are as high as 3000) encoding for transcription factors in the human genome (~10% of all human genes). These genes tend to be highly conserved and, in many instances, can be functionally interchangeable between organisms of different clades.

Structure

Like all proteins, transcription factors are composed of discrete functional modules called "domains". Transcription factors generally contain at least two functional domains, a DNA binding domain (DBD) and a trans-activating domain (TAD). Some transcription factors also possess a signal sensing domain (SSD).