transcription factor

A transcription factor is a protein that reads the genome from the outside and decides how loudly a gene should be heard. It recognises a short DNA sequence, grabs onto it, and then either helps switch a gene on or holds it down — a molecular hand on the dial.

Each transcription factor has a part that binds specific DNA shapes or sequences and another part that talks to the transcription machinery or to other proteins. Activators recruit and stabilise RNA polymerase to boost transcription; repressors block it. Many factors only act when a signal flips them — a hormone binds, a phosphate group is added — so the cell can respond to its surroundings by changing which genes it expresses.

Transcription factors rarely work solo. Combinations of factors binding nearby create a code, so the presence of factor A plus factor B but not C might mean “express this gene in muscle.” This combinatorial logic lets a few hundred such proteins orchestrate the precise expression of thousands of genes across every cell type.