Difference between RNA Polymerase I II and III

The synthesis of mRNA is a complex process in eukaryotes. In comparison to prokaryotes, where only a single polymerase is required to bind with the DNA strands, eukaryotes require three different polymerases, along with an additional set of transcriptional factors (TFs) for transcription and translation. The three polymerases required are RNA polymerase I, RNA polymerase II and RNA polymerase III.

RNA Polymerase I

RNA Polymerase I, also known as Pol I, is an enzyme that transcribes ribosomal RNA. It is composed of 14 subunits and weighs around 590 kDa. It transcribes the subunits of rRNA except for the 5S rRNA subunit. The transcription by Pol I accounts for about 50% of the total transcription in a cell.

Refer: Structure, Functions and Types of RNA

RNA Polymerase II

RNA Polymerase II, also known as Pol II, is an enzyme that transcribes all the precursors of mRNA, miRNA and snRNA. It is composed of 12 subunits and weighs 550kDa. It requires an assembly of transcription factors to begin transcription.

𝛂-Amanitin is a toxin produced by mushrooms that inhibits Pol II. It renders the enzyme totally unresponsive.

RNA Polymerase III

RNA Polymerase III, also known as Pol III, transcribes tRNA and the 5S subunit of ribosomal RNA. It is composed of 17 subunits and weighs around 700 kDa. The genes transcribed by Pol III are directly in association with cell cycle and cell growth, therefore this enzyme needs to be active at all times and in every environment. Pol III does not require a heavy assemblage of TFs like Pol II.

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Also Visit:

• DNA Polymerase: Structure, Types and Functions
• Principle, Steps, Types, Components And Applications Of PCR
• Stages Of Transcription, RNA Polymerase