Difference Between Prokaryotic and Eukaryotic RNA Polymerase

The main difference between prokaryotic and eukaryotic RNA polymerase is that prokaryotes have a single type of RNA polymerase, whereas eukaryotes have three main types of RNA polymerases. Furthermore, prokaryotic RNA polymerase contains five subunits while in eukaryotes, RNA polymerase I transcribes rRNA genes, RNA polymerase II transcribes mRNA genes, and RNA polymerase III transcribes small RNA genes such as genes for tRNAs. 

Prokaryotic and eukaryotic RNA polymerase are the two types of RNA polymerases present in organisms. Prokaryotes regulate transcription with the use of different types of sigma factors while eukaryotic transcription is regulated by the presence of different types of RNA polymerases. 

Key Areas Covered 

1. What is Prokaryotic RNA Polymerase
     – Definition, Structure, Importance
2. What is Eukaryotic RNA Polymerase
     – Definition, Types, Importance
3. What are the Similarities Between Prokaryotic and Eukaryotic RNA Polymerase
     – Outline of Common Features
4. What is the Difference Between Prokaryotic and Eukaryotic RNA Polymerase
     – Comparison of Key Differences

Key Terms 

Eukaryotic RNA Polymerase, Prokaryotic RNA Polymerase, RNA Pol II, Sigma Factor, Transcription

What is Prokaryotic RNA Polymerase 

The prokaryotic RNA polymerase is the single type of RNA polymerase responsible for prokaryotic transcription. The complete holoenzyme of prokaryotic RNA polymerase consists of five subunits; β’βαI and αIIωσ. There are distinct sigma factors which oversee the transcription of specific sets of genes. Moreover, they can be distinguished by the distinct sets of promoters to which these transcription factors bind.

Figure 1: Thermus aquaticus RNA Polymerase

Furthermore, the four types of catalytic subunits of prokaryotic RNA polymerase include β’, β, α, and ω Here, the largest subunit is β’, which contains a part of the active center responsible for RNA synthesis. Moreover, the second-largest subunit is β, which contain the rest of the active center responsible for RNA synthesis. In addition, the third-largest subunit is the α subunit present in two copies per molecule of RNAP, αI and αII each containing two domains; αNTD and αCTD. The former domain contains determinants for assembly of RNAP while the latter domain contains determinants for interaction with promoter DNA. However, the smallest subunit is the ω subunit, which facilitates assembly of RNAP and stabilizes assembled RNAP. However, the sigma factor is the transcription initiation factor which binds to the catalytic core of prokaryotic RNA polymerase, increasing the specificity for promoters.  

What is Eukaryotic RNA Polymerase 

The eukaryotic RNA polymerase is the group of enzymes responsible for the transcription in eukaryotes. Generally, eukaryotic transcription is more complex than prokaryotic transcription. Moreover, this is achieved by the presence of different types of RNA polymerases to transcribe specific types of RNA genes. Furthermore, the three main types of RNA polymerases in eukaryotes are RNA pol I responsible for the transcription of rRNA, RNA pol II responsible for the transcription of mRNA, and RNA pol III responsible for the transcription of tRNA, rRNA 5S, and other small RNAs.

Figure 2: RNA Pol II

Moreover, there are other two types of RNA polymerases. Basically, RNA pol IV is responsible for the transcription of siRNA in plants and RNA pol V is responsible for the transcription of RNAs in siRNA-directed heterochromatin formation in plants.  

Similarities Between Prokaryotic and Eukaryotic RNA Polymerase  

• Prokaryotic and eukaryotic RNA  polymerase are the two types of RNA polymerases that occur in prokaryotes and eukaryotes.  
• Furthermore, they are the enzymes responsible for transcription in which genetic information in genes is copied to RNA molecules.  
• Both are DNA-directed  RNA polymerases.    
• Before transcription,  transcription factors bind to the promoter region to initiate the unwinding of DNA. Moreover, this recruits RNA polymerase to the DNA  template.  
• In addition, RNA polymerases can be either multisubunit enzymes or single subunit enzymes. 

Difference Between Prokaryotic and Eukaryotic RNA Polymerase 

Definition 

Prokaryotic RNA polymerase refers to the RNA polymerase in prokaryotes, consisting of four subunits and a sigma factor while eukaryotic RNA polymerase refers to the five types of RNA polymerases occur in eukaryotes.  

Significance 

A single type of RNA polymerase is responsible for prokaryotic transcription while the five types of eukaryotic RNA polymerases are RNA pol I, II, III, IV, and V. 

Subunits 

Prokaryotic RNA polymerase core enzyme contains five subunits while eukaryotic RNA polymerases contain 10-20 subunits. 

Size 

Moreover, the size of the prokaryotic RNA polymerase is around 400 kDa while the size of the eukaryotic RNA polymerase is 500 kDa. 

Type of Transcription 

Prokaryotic RNA polymerase synthesizes polycistronic RNA while eukaryotic RNA polymerase synthesizes monocistronic RNA. 

Regulation of Transcription 

While prokaryotes regulate transcription with the use of different types of sigma factors, eukaryotic transcription is regulated by the presence of different types of RNA polymerases. 

Conclusion 

Basically, the prokaryotic RNA polymerase is the enzyme responsible for the transcription in prokaryotes. Moreover, prokaryotes contain only a single type of RNA polymerase with multi subunits. In addition, they regulate transcription by the binding of different types of sigma factors to the enzyme. In contrast, eukaryotic RNA polymerase refers to a group of enzymes responsible for the transcription in eukaryotes. However, RNA pol I transcribes rRNA, RNA pol II transcribes mRNA, and RNA pol III transcribes tRNA. Therefore, the main difference between prokaryotic and eukaryotic RNA polymerase is the number of enzymes present and the regulation of transcription. 

References:

1. Clancy, S. (2008) RNA transcription by RNA polymerase: prokaryotes vs eukaryotes. Nature Education 1(1):125. Available Here.

Image Courtesy:

1. “RNAP TEC small” By User:Abbondanzieri on the English Wikipedia – Created with the rendering program Protein Explorer using coordinates 1H38 deposited at the RCSB PDB repository. (Public Domain) via Commons Wikimedia   
2. “Alpha-Amanitin–RNA polymerase II complex 1K83” By Fvasconcellos 21:15, 14 November 2007 (UTC) – From PDB entry 1K83. (Public Domain) via Commons Wikimedia