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[Biochemistry](https://durgical.com/en/biochemistry/) · Topic

# Transcription

Transcription copies a DNA gene into an RNA molecule; in eukaryotes three RNA polymerases do it with the help of transcription factors.

Updated 2026-11-01

## Key facts

- RNA polymerase reads the template strand 3'→5' and makes RNA 5'→3'; it needs no primer and does not proofread.
- Pol I: 28S, 18S and 5.8S rRNA (nucleolus). Pol II: mRNA, most snRNAs and microRNAs. Pol III: tRNA, 5S rRNA.
- Pol II promoter: TATA box (about −25 to −30) and elements such as CAAT and GC boxes; enhancers can lie far away.
- TFIID (with the TATA-binding protein, TBP) binds first; TFIIH opens the DNA and phosphorylates Pol II's C-terminal domain (CTD).
- Rifampicin inhibits bacterial RNA polymerase; α-amanitin inhibits human Pol II.

## In detail

- Initiation: the general factors (TFIID, TFIIA, TFIIB, TFIIF, TFIIE, TFIIH) and Pol II form the preinitiation complex on the promoter.
- Phosphorylation of CTD serine 5 releases the polymerase from the promoter and recruits the capping enzyme; phosphorylated serine 2 recruits splicing and polyadenylation factors.
- Elongation: the transcription bubble moves along with about 17 bp open; the RNA–DNA hybrid is about 8–9 bp long.
- Termination in eukaryotes: after the AAUAAA signal the RNA is cut and the polymerase falls off. In bacteria: a GC-rich hairpin followed by U's, or the rho factor.
- Activators bind enhancers and, through Mediator, help assemble the machinery; repressors and silencers do the opposite.
- Bacteria have a single RNA polymerase (α₂ββ'ω) that finds the promoter with the σ factor (−10 Pribnow and −35 boxes).

## Clinical notes

- Rifampicin, a backbone of tuberculosis treatment, blocks the β subunit of bacterial RNA polymerase; rpoB mutations cause resistance.
- Amanita mushroom poisoning shuts down Pol II in the liver and causes hepatic necrosis.
- Actinomycin D intercalates into DNA and stops transcription; it is used in some childhood tumours.

## Related conditions

- [Tuberculosis](https://durgical.com/en/conditions/tuberculosis/)

## Related

- [RNA polymerases I, II and III](https://durgical.com/en/biochemistry/enzymes/rna-polymerases-i-ii-and-iii/)
- [RNA processing (cap, poly-A tail and splicing)](https://durgical.com/en/biochemistry/topics/rna-processing/)
- [Central dogma of molecular biology](https://durgical.com/en/biochemistry/topics/central-dogma-of-molecular-biology/)
- [The lac operon and gene regulation in bacteria](https://durgical.com/en/biochemistry/topics/the-lac-operon-and-gene-regulation-in-bacteria/)
- [Epigenetics: DNA and histone methylation](https://durgical.com/en/biochemistry/topics/epigenetics-dna-and-histone-methylation/)
- [α-Amanitin](https://durgical.com/en/biochemistry/molecules/amanitin/)

## Test yourself

Think of the answer, then tap the question to see it.

## Which eukaryotic RNA polymerase makes mRNA, and what is its classic toxin?

RNA polymerase II; it is inhibited by α-amanitin from Amanita mushrooms.

## What does TFIIH do at transcription initiation?

It opens the double helix with its helicase activity and phosphorylates Pol II's CTD so it leaves the promoter.

## How does RNA polymerase differ from DNA polymerase regarding primers?

RNA polymerase starts without a primer; DNA polymerase needs a free 3'-OH.

## Which antituberculosis drug inhibits bacterial transcription?

Rifampicin, which binds the β subunit (rpoB) of bacterial RNA polymerase.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Gene expression (Transcription)](https://reactome.org/PathwayBrowser/#/R-HSA-74160) (Reactome, 2026); [RNA Polymerase II Transcription](https://reactome.org/PathwayBrowser/#/R-HSA-73857) (Reactome, 2026); [How do genes direct the production of proteins?: MedlinePlus Genetics](https://medlineplus.gov/genetics/understanding/howgeneswork/makingprotein/) (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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