The main difference between prokaryotic and eukaryotic promoters is that prokaryotic promoters contain two hexameric motifs near 10 and −35 positions relative to the TSS (transcription start site), whereas eukaryotic promoters are more complex and have several motifs.
Prokaryotic and eukaryotic promoters are two promoter types that occur in organisms. Their function is to bind RNA polymerase to initiate transcription.
Key Areas Covered
1. What are Promoters
– Definition, Structure, Importance
2. What are Prokaryotic Promoters
– Definition, Structure, Importance
3. What are Eukaryotic Promoters
– Definition, Structure, Importance
4. Similarities Between Prokaryotic and Eukaryotic Promoters
– Outline of Common Features
4. Difference Between Prokaryotic and Eukaryotic Promoters
– Comparison of Key Differences
Key Terms
Eukaryotic Promoters, Prokaryotic Promoters
What are Promoters
Promoters are one of the main regulatory elements of the gene which initiates the transcription. It is located near the gene, upstream of the codon sequence. The size of the promoter can be 100-1000 bp. The specific DNA sequences called response elements provide initial binding sites for both RNA polymerase and transcription factors which recruit RNA polymerase. RNA polymerase is the enzyme responsible for the transcription, polymerizing complementary RNA nucleotides to synthesize a mRNA molecule.
Importantly, bacterial RNA polymerase associated with the sigma factor can bind to the promoter. The sigma factor is a bacterial transcription initiation factor. Around 7 different basal transcription factors in eukaryotes have to be bound to the promoter to recruit RNA polymerase. Typically, promoters contain sequence motifs whose positions are relative to the transcription start site.
What are Prokaryotic Promoters
Prokaryotic promoters are the DNA sequences that bind to the RNA polymerase to initiate transcription in prokaryotes. Significantly, they contain two hexameric motifs in −10 and −35 positions relative to the transcription start site. Therefore, they are simple promoters.
Figure 1: Prokaryotic Promoter
Furthermore, the sequence that occurs at -10 is the Pribnowbox. It contains six nucleotides. They are TATAAT. It is absolutely important for the start of transcription in prokaryotes. In comparison, the -35 element of the prokaryotic promoter consists of six nucleotides that are TTGACA. The presence of the -35 element provides a very high transcription rate.
What are Eukaryotic Promoters
Eukaryotic promoters are the DNA sequences that bind to the RNA polymerase in eukaryotes to initiate transcription. However, eukaryotic promoters are more complex than prokaryotic promoters. Also, several different sequence motifs occur in the eukaryotic promoters. They include the TATA box, INR box, BRE, CCAAT box, and GC box.
Figure 2: Eukaryotic Promoter
Moreover, eukaryotic promoters are difficult to characterize due to their complexity. Also, their sequence motifs occur several kilobases away from the transcription start site. Therefore, DNA bends at the promoter site in eukaryotic promoters while binding the regulatory sequences to the transcription start site. Further, the TATA box, a sequence motif of the eukaryotic promoter, binds with the TATA-binding proteins. It assists in the formation of RNA polymerase transcriptional complex. Also, the TATA box occurs very close to the transcription start site. Its DNA sequence is TATAAA.
Similarities Between Prokaryotic and Eukaryotic Promoters
- Prokaryotic and eukaryotic promoters are two promoters that occur in different organisms.
- Their function is to initiate transcription by binding to RNA polymerase.
- They occur upstream to the transcription start site. They are bendable.
Difference Between Prokaryotic and Eukaryotic Promoters
Definition
Prokaryotic promoters refer to the promoters consisting of two short sequences at -10 and -35 positions upstream from the transcription start site. In contrast, eukaryotic promoters refer to complex structures that bind to the RNA polymerase to initiate transcription.
Complexity
Prokaryotic promoters are simple, while eukaryotic promoters are complex.
Sequence Motifs
Prokaryotic promoters contain two hexameric motifs near -10 and −35 positions relative to the TSS. In contrast, eukaryotic promoters contain different sequence motifs, including TATA box, INR box, BRE, CCAAT-box, and GC-box.
Occurrence of the Sequence Motifs
Prokaryotic promoters contain their sequence motifs several bases away from the transcription start site, while eukaryotic promoters contain their sequence motifs several kilobases away from the transcription start site.
Bending
Prokaryotic promoters do not bend, while eukaryotic promoters bend.
Genes or Operons
Prokaryotic promoters regulate the expression of operons, while eukaryotic promoters regulate the expression of genes.
Conclusion
In brief, prokaryotic and eukaryotic promoters are two promoter types that occur in organisms. They initiate the transcription by binding to RNA polymerase. Prokaryotic promoters are simple DNA sequences. They contain two hexameric motifs near 10 and −35 positions relative to the TSS. Also, the sequence motifs occur several bases away from the transcription start site. Additionally, prokaryotic promoters do not bend. In comparison, eukaryotic promoters are complex. They contain several sequence motifs, including the TATA box, INR box, BRE, CCAAT box, and GC box. However, sequence motifs occur several kilobases away from the transcription start site. But eukaryotic promoters bend. Therefore, the main difference between prokaryotic and eukaryotic promoters is their sequence motifs.
References:
- Kanhere A, Bansal M. Structural properties of promoters: similarities and differences between prokaryotes and eukaryotes. Nucleic Acids Res. 2005 Jun 6;33(10):3165-75. doi: 10.1093/nar/gki627. PMID: 15939933; PMCID: PMC1143579.
Image Courtesy:
- “Figure 16 02 02” By CNX OpenStax – Own work (CC-BY 4.0) via Commons Wikimedia
- “Figure 16 04 01.” By CNX OpenStax – Own Work (CC-BY 4.0) via Commons Wikimedia
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