Transcription factor

A transcription factor is a protein that regulates transcription, the copying of a gene's DNA into RNA. Most recognize and bind short DNA sequences in or near the genes they control. In eukaryotes, RNA polymerase cannot start transcription by itself: general transcription factors, such as TFIID, which binds the TATA box, must first gather at the core promoter and position the polymerase.

Specific transcription factors adjust the rate. Activators bound to enhancers, which may lie thousands of base pairs from the gene, reach the promoter as the DNA bends into a loop and boost transcription, while repressors reduce it. Each factor has a DNA-binding region, often built on a common shape such as a zinc finger, a helix-turn-helix or a leucine zipper, and usually another region that recruits other proteins. Many respond to signals: a steroid hormone receptor becomes an active transcription factor once it binds its hormone.

Because each cell type uses its own combination of transcription factors, one genome can produce neurons, muscle and blood cells. Hox proteins pattern the body during development, and four factors, OCT4, SOX2, KLF4 and MYC, can reprogram adult cells into induced pluripotent stem cells. Faulty transcription factors underlie many diseases, including cancers driven by MYC or by loss of the tumor suppressor p53.