RNA polymerases are enzymes responsible for transcribing DNA into RNA. Different types of RNA polymerases exist in eukaryotes and prokaryotes, each with its specific functions and promoter recognition sequences.
* RNA polymerase (RNAP): The single RNA polymerase in prokaryotes transcribes all types of RNA (mRNA, tRNA, rRNA).
* Promoter Structure:
* -10 element (Pribnow box): TATAAT sequence located about 10 base pairs upstream from the transcription start site.
* -35 element: TTGACA sequence located about 35 base pairs upstream from the transcription start site.
* Upstream elements: Some promoters have additional elements further upstream, influencing transcription efficiency.
* RNA polymerase I (Pol I): Responsible for transcribing ribosomal RNA (rRNA) genes.
* Promoter Structure:
* Core promoter: A region containing a core element and an upstream control element (UCE).
* Core element: A short sequence located about 40 bp upstream of the transcription start site.
* UCE: A region located approximately 100 bp upstream of the transcription start site, often containing a conserved sequence called the "upstream element" (UE).
* RNA polymerase II (Pol II): Transcribes protein-coding genes (mRNA) and some small nuclear RNA (snRNA) genes.
* Promoter Structure:
* Core promoter: Typically contains the following elements:
* TATA box: A conserved sequence located about 25-30 bp upstream of the transcription start site.
* Initiator (Inr): A sequence located around the transcription start site.
* Downstream promoter element (DPE): Located downstream of the transcription start site.
* BRE (TFIIB recognition element): A sequence located upstream of the TATA box, recognized by transcription factor IIB (TFIIB).
* Upstream regulatory elements: These elements can be located hundreds or even thousands of base pairs upstream of the core promoter and influence the rate of transcription. Examples include:
* CAAT box: A consensus sequence that binds transcription factors.
* GC box: A GC-rich sequence recognized by transcription factors.
* Enhancers: DNA sequences that can stimulate transcription, often located far from the core promoter.
* RNA polymerase III (Pol III): Transcribes transfer RNA (tRNA), 5S ribosomal RNA (5S rRNA), and some small nuclear RNA (snRNA) genes.
* Promoter Structure:
* Internal promoter: Located within the transcribed region for tRNA and 5S rRNA genes.
* Upstream promoter: Located upstream of the transcribed region for some snRNA genes.
| RNA Polymerase | Transcripts | Promoters |
|---|---|---|
| Prokaryotic RNAP | mRNA, tRNA, rRNA | -10 element, -35 element, upstream elements |
| Eukaryotic Pol I | rRNA | Core promoter, UCE |
| Eukaryotic Pol II | mRNA, some snRNA | Core promoter (TATA box, Inr, DPE, BRE), upstream regulatory elements |
| Eukaryotic Pol III | tRNA, 5S rRNA, some snRNA | Internal promoter (for tRNA, 5S rRNA), upstream promoter (for some snRNA) |
This table is not exhaustive, as different types of promoters and their regulatory elements exist within each group. The specific sequences and structures of promoters can vary, influencing the efficiency and regulation of transcription.
