“The RNA polymerase is an enzyme that catalyzes the synthesis reaction of ribonucleic acid-RNA.”
The polymerases are the class of enzymes that regulate the reaction of nucleic acid synthesis viz synthesis of DNA by DNA polymerase and synthesis of RNA by RNA polymerase.
RNA polymerase is an enzyme that is responsible for the transcription process. Unlike prokaryotes where a single RNA polymerase facilitates transcription, there are three types of RNA polymerases in eukaryotes that play different roles in the process of making RNA from DNA.
Structure of RNA polymerase:
The structure of all three polymerases that are found in eukaryotes has a catalytic core consisting of 10 subunits. 5 subunits form a crab claw shape at the center of the DNA forming the channels for the RNA products as well as for the NTP substrates.
This claw-like shape helps DNA to stabilize as well as for correcting formation of the transcription bubble.
Among all three RNAPs, RNA pol II is a preliminary enzyme for the formation of mRNA during the transcription. It has a total of 12 subunits, along with10 subunits are those that are found in all of the RNA polymerases, RNA pol II has an extra two subunits of Rpb4/7 which initiates the transcription and also helpful in post-transcriptional modification.
The function of RNA polymerase:
Because RNA pol II is responsible for the synthesis of mRNA, it is functioning in the process of transcription.
There are five general transcription factors required to initiate the process of RNA polymerase II to form the mRNA.
Promoter region and TATA box bound to the TFIID, the transcription factor initiates the transcription process. After that TFIIB binds to TFIID and that forms a bridge for RNA pol II. That begins the process of transcription.
RNAP binds to the promoter site of DNA with other transcription factors and forms a transcription pre-initiation complex to start the transcription initiation.
The promoter is a site located at 5’ DNA strand and in that TATA rich sequence that is recognized by RNAP II.
Transcription factors bind to the TATA box causing a change in the shape of the DNA strand that allows other transcription proteins to come and bind with RNA pol II that make the transcription initiation complex.
RNA polymerase always builds RNA strands from 5’ to 3’ site.
Related article: Comparison Between DNA Polymerase Vs RNA Polymerase.
Elongation of transcription:
In elongation, the RNA strand gets longer and complementary nucleotides are added to the strand. Phosphate groups are added to the tail end of RNAP II by TFIIH, releasing the enzyme so they can start the second round of transcription.
For the second round of transcription, the transcriptional factors are released and then recycled. After completion of the entire process, the phosphatase removes the phosphate group from the RNAP II.
- RNAP I – responsible for the synthesis of rRNA
- RNAPIII – responsible for the synthesis of t-RNA
Termination of transcription:
Once the RNA polymerase reachers to the end of the process, there is a special type of termination sequences located at the end that gives signals to RNAP to stop transcription.
Read more: Multifunctional DNA Polymerase: An Overview.
The process of transcription which is governed by the RNA polymerase is totally different from the reaction govern by the DNA polymerase. As it forms the RNA it doesn’t require any of the starting sequencings to make a polynucleotide chain. Therefore the process governs by the RNA polymerase is de novo.