Promotor

In genetics, a promoter (originally French: promoteur, instigator, initiator) is a section of DNA that controls the expression of a gene. As a transcription start point, this section determines the timing and frequency of gene expression. The promoter binds an enzyme (RNA polymerase), which reads the gene sequence and produces an RNA copy (see illustration). The promoter region contains recognition sequences for the transcription enzyme complex and for regulatory proteins.

Most genes are preceded by a promoter, which is divided into three parts: the enhancer, the proximal promoter and the core promoter (viewed from the 5' end). The core promoter usually contains the TATA box, which is essential for transcription. It is the crucial point that is necessary for transcription to start at all, because this is where the transcription factors bind. TATA refers to the base sequence thymine - adenine - thymine - adenine.

The promoter is located upstream of the area of the respective gene to be read (it no longer belongs to it and is not read). It is located upstream of the gene (at the 5' end of the non-matrix strand and thus in the direction of synthesis upstream of the RNA-coding region. The most important property of a promoter is its specific interaction with certain DNA-binding proteins, which mediate the start of transcription of the gene by the RNA polymerase and are known as transcription factors.

The promoter is part of the "(gene) regulatory regions". They also include nucleotide sequences further away from the gene, which can nevertheless influence its expression. The enhancer is intended to increase the transcription of the DNA by enabling additional binding sites of the transcription complex to the gene. In addition to enhancers, there are also silencers, which have the exact opposite effect. Enhancers and silencers are also referred to as cis-elements (Latin 'cis' = 'on the same side as') (Kundaje A et al. 2015).

Bacterial promoters have a relatively uniform structure, with rather limited differences in the exact nucleotide sequence. They are also referred to as strong or weak promoters depending on the sequence. The strength of a promoter can be predicted by comparing it with a consensus sequence of different promoters.

Eukaryotic promoters, on the other hand, are characterized by strong differences between them. Although there are some widespread elements such as the downstream promoter element, a general eukaryotic promoter-specific nucleotide sequence is difficult to characterize. It is therefore not easy to characterize them using bioinformatic methods, for example in gene prediction. For this reason, promoters are now primarily mapped using high-throughput methods. The integrative analysis of RNA-Seq data, DNA accessibility for DNases, histone modification and DNA methylation allows the cell- or tissue-specific identification of promoters in whole genomes (Kundaje A et al. 2015).

1. Campbell Biology 10th, updated edition; Reece et al; Fig. 17.8
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4. Paget MS (2015) Bacterial Sigma Factors and Anti-Sigma Factors: Structure, Function and Distribution. In: Biomolecules 5: 1245-1265.