A promoter is a regulatory region of DNA located upstream (towards the 5' region) of of a gene, providing a control point for regulated gene transcription.

The promoter contains specific DNA sequences that are recognized by proteins known as transcription factors. These factors bind to the promoter sequences, recruiting RNA polymerase, the enzyme that synthesizes the RNA from the coding region of the gene.

PROMOTER ELEMENTS

1. Core promoter - the minimal portion of the promoter required to properly initiate transcription

• Transcription Start Site (TSS)
• Approximately -34
• A binding site for RNA polymerase
• General transcription factor binding sites

2. Proximal promoter - the proximal sequence upstream of the gene that tends to contain primary regulatory elements

• Approximately -250
• Specific transcription factor binding sites

Difference between Eukaryotic and Prokaryotic Promoters

Prokaryotic promoters

In prokaryotes, the promoter consists of two short sequences at -10 and -35 positions upstream from the transcription start site.

Eukaryotic promoters

Eukaryotic promoters are extremely diverse and are difficult to characterize. They typically lie upstream of the gene and can have regulatory elements several kilobases away from the transcriptional start site. In eukaryotes, the transcriptional complex can cause the DNA to bend back on itself, which allows for placement of regulatory sequences far from the actual site of transcription. Many eukaryotic promoters, contain a TATA box (sequence TATAAA), which in turn binds a TATA binding protein which assists in the formation of the RNA polymerase transcriptional complex. The TATA box typically lies very close to the transcriptional start site (often within 50 bases).