---
title: "Transcription Initiation: Promoters, General Factors and Polymerase Recruitment"
description: "Eukaryotic polymerase does not find a promoter alone: general factors assemble on it first and position the enzyme at the start site. The rate of transcription is set mostly at this assembly step."
canonical: https://lightmysky.com/learn/science/transcription-initiation-promoters-general-factors-and-polymerase-recruitment-mt_0Ky-pYgh0Y
source: https://lightmysky.com/learn/science/transcription-initiation-promoters-general-factors-and-polymerase-recruitment-mt_0Ky-pYgh0Y.md
retrieved: 2026-09-12
---

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# Transcription Initiation: Promoters, General Factors and Polymerase Recruitment

Eukaryotic polymerase does not find a promoter alone: general factors assemble on it first and position the enzyme at the start site. The rate of transcription is set mostly at this assembly step.

Subject: Science · Area: Biochemistry & Molecular Biology · Ages 19 to 21
Page: https://lightmysky.com/learn/science/transcription-initiation-promoters-general-factors-and-polymerase-recruitment-mt_0Ky-pYgh0Y

## Ready when they can

- Describes assembly at a promoter in order and says which step commits the enzyme.
- Explains why initiation, rather than elongation, is the usual control point.
- Contrasts the bacterial single-factor arrangement with the eukaryotic assembly.

## Lesson: Assemble first, then read

Eukaryotic polymerase does not find a promoter alone: general factors assemble on it first and position the enzyme at the start site. TFIID grips the TATA box, TFIIA and TFIIB stabilise it, then polymerase arrives with TFIIF, followed by TFIIE and TFIIH. Each factor enables the next, like a checklist.

TFIIH finishes the job twice over: its helicase activity melts the promoter into an open complex, and its kinase phosphorylates the polymerase tail. That phosphorylation licenses promoter escape, the moment the enzyme breaks its initiation contacts and commits to the gene. Without it the enzyme idles at the start and no mRNA results.

Because initiation decides whether any RNA is made at all, cells regulate here rather than mid-gene. Blocking one promoter shuts off its whole gene cleanly, while stopping elongation would waste a half-built transcript and jam the template. Activators recruit or stabilise the complex and repressors block assembly or escape, setting each promoter's firing rate.

**Tip.** Bacteria run the same errand with striking economy: a single sigma factor guides polymerase to the minus 10 and minus 35 promoter elements. One protein provides the specificity that eukaryotes distribute across a dozen general factors. Regulation then reduces to helping or hindering sigma binding.

**Recap.** Factors assemble in order, escape commits the enzyme, and control lives at the start.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Transcription and RNA Splicing in Eukaryotes](https://lightmysky.com/learn/science/transcription-and-rna-splicing-in-eukaryotes-mt_j2vc70vH5t)
- [Homologous Recombination and Double-Strand Break Repair](https://lightmysky.com/learn/science/homologous-recombination-and-double-strand-break-repair-mt_yWlwqAsXEf)

## Opens up

- [Enhancers, Accessibility and Combinatorial Control](https://lightmysky.com/learn/science/enhancers-accessibility-and-combinatorial-control-mt_BTMCj6V6jD)
- [Sleep, Circadian Rhythms and the Clock in the Brain](https://lightmysky.com/learn/science/sleep-circadian-rhythms-and-the-clock-in-the-brain-mt_cXx4SaLJUM)
- [Operon Logic: Induction, Repression and Feedback on Transcription](https://lightmysky.com/learn/science/operon-logic-induction-repression-and-feedback-on-transcription-mt_yNvJjGMSJQ)