Describe the components of the promoter region of a eukaryotic gene

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In eukaryotic genes, the promoter region is a special stretch of DNA that lies just before the gene. Its main job is to control when and where transcription starts. It does this by providing binding sites for RNA polymerase II and other transcription factors.

The promoter region can be divided into two main parts:

Core Promoter
Proximal Promoter Elements

Each of these parts has different types of DNA sequences that help start and regulate transcription.

1. Core Promoter

This is the most essential part of the promoter and lies near the transcription start site (called the +1 position). It directly helps in assembling the transcription machinery. The core promoter usually includes the following elements:

TATA Box:

A short DNA sequence (TATAAA) usually located 25–35 base pairs upstream from +1 site. It helps in positioning RNA polymerase II. A special protein called TBP (TATA-binding protein) binds here to start the transcription complex.

Initiator (Inr) Sequence:

Found around the +1 site. It helps start transcription at the correct location. Some promoters have Inr even if they do not have a TATA box.

BRE (TFIIB Recognition Element):

Found either just upstream or downstream of the TATA box. It binds the TFIIB protein which supports recruitment of RNA polymerase II.

DPE (Downstream Promoter Element):

Found downstream of the transcription start site (usually at +28 to +32). Especially useful in promoters that lack a TATA box.

2. Proximal Promoter Elements

These are found a little further upstream of the core promoter. They help enhance the level of transcription by binding extra transcription factors.

CAAT Box:

Located around 75 base pairs upstream. It binds proteins like NF-Y which increase transcription strength.

GC Box:

A region rich in guanine and cytosine. It binds the Sp1 protein and supports basic transcription activity. These are often present in housekeeping genes.

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