# Switching genes on: transcription factors

> Proteins called transcription factors read short DNA switches and decide which genes are copied, in which cells, and when.

Source: https://khushisingh.in/explore/02-switching-genes-on/
Author: Khushi Singh (khushisingh.in). Licence: CC BY 4.0 for text and original illustrations, unless a credit says otherwise.
Evidence labels used on this site: established, strong evidence, emerging, hypothesis, debated. Where a page has Simple, Curious and Expert versions, all three follow.

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[Biology made simple](https://khushisingh.in/explore/) · How genes work · 2 of 8

About 2 minutes

**Transcription factors** are proteins that recognise short DNA sequences, a few letters long. They sit on **enhancers**, switches near or far from a gene, and help RNA polymerase start at the gene’s **promoter**; other factors keep genes off. (evidence: established)

The idea was first worked out in bacteria, which switch on the genes for digesting a sugar only when that sugar is around (Jacob & Monod 1961). Plants use factors to decide when to flower, and humans have more than 1,600 of them (Lambert et al. 2018). Each cell type makes its own mix, so each switches on its own genes.

*[Here the web page has an interactive activity; open the source URL to use it.]*

**In my research:** [The factors and complexes that control genes in early development →](https://khushisingh.in/research/interests/#chromatin)

## Sources

1. Jacob F, Monod J (1961) Genetic regulatory mechanisms in the synthesis of proteins. Journal of Molecular Biology 3:318–356. [doi:10.1016/S0022-2836(61)80072-7](https://doi.org/10.1016/S0022-2836(61)80072-7)
2. Lambert SA, et al. (2018) The human transcription factors. Cell 172:650–665. [doi:10.1016/j.cell.2018.01.029](https://doi.org/10.1016/j.cell.2018.01.029)