RNA Polymerase: Check Structure, Types and Function

What Is RNA Polymerase?

It is a very important enzyme which synthesises RNA from a DNA template in a process called transcription. It reads the DNA sequence for a gene and produces the corresponding RNA sequence, which either goes on to make proteins or performs other cellular functions. This enzyme works by first unwinding the double helix of DNA before assembling RNA nucleotides into a string, based upon the complementary DNA sequence.

Latest: NEET 2024 Paper Analysis and Answer Key 

Don't Miss: Most scoring concepts for NEET | NEET papers with solutions

New: NEET Syllabus 2025 for Physics, Chemistry, Biology

NEET Important PYQ & Solutions: Physics | Chemistry | Biology | NEET PYQ's (2015-24)

The role of the enzyme RNA Polymerase in the expression of genes can be said to be very essential. Without this enzyme, cells will not be able to transcribe the genetic information residing in the DNA and program it into useful molecules. RNA Polymerase helps cells transcribe proper genes at the relevant time and keeps the cell functioning in response to changes in the environment. The process is indispensable and vital for growth, development, and general adaptation in the living body.

This article will be concerned with a detailed analysis of RNA Polymerase, including its structure, functions, mechanisms, and its relation to health and disease. We shall consider the types of RNA Polymerase present in prokaryotic and eukaryotic cells, discuss the control of its functioning, and its importance in various areas of biology. Experimental techniques for the study of RNA Polymerase will be addressed, paying importance to medical research and treatment.

Structure Of RNA Polymerase

RNA polymerase is a multi-subunit enzyme. It is a protein consisting of a collection of protein subunits that come together to carry out the activities of an enzyme. In prokaryotes, the core polymerase comprises five subunits: two alpha, one beta, one beta prime, and one omega. The enzyme consists of three subunits—β and β', which together form the catalytic centre, and α, which is involved in assembly and regulation.

Comparison Of Prokaryotic And Eukaryotic RNA Polymerase

Prokaryotic versus eukaryotic RNA Polymerases are less complicated than eukaryotic ones and also compared to the prokaryotic ones and others in regards to their functions.

Prokaryotic RNA Polymerase (Core Enzyme, Sigma Factor)

In prokaryotes, RNA Polymerase needs an additional subunit called the sigma (σ) factor for initiation of transcription. This σ factor binds to specific promoter regions on the DNA, thus positioning the core enzyme to start RNA synthesis.

Eukaryotic RNA Polymerase (Types i, ii, And iii)

Eukaryotes have three different types of RNA Polymerase, each transcribing different gene classes:

• RNA polymerase I transcribes rRNA genes.

• RNA polymerase II transcribes mRNA and some snRNAs.

• RNA polymerase III transcribes tRNA, 5S rRNA, and other small RNAs.

These differences mirror the greater complexity and specialisation of eukaryotic transcription machinery compared to that of prokaryotes.

Functions Of RNA Polymerase

The function of RNA Polymerase include:

Role In Transcription

• Initiation: The binding of RNA Polymerase to the promoter region of a gene, aided by several transcription factors, initiates transcription.

• Elongation: The enzyme moves along the DNA template, synthesizing RNA by adding nucleotides matching the DNA sequence.

• Termination: The process ends with the termination signal, and when the RNA Polymerase reaches a termination site, the newly synthesised RNA is released from the template.

RNA Synthesis

• The mechanism of RNA synthesis goes through the steps as follows :

• RNA Polymerase binds to DNA at the promoter.

• The enzyme unwinds the DNA helix.

• RNA nucleotides are joined together in a continuous RNA strand.

• The RNA strand continues to grow in length until a termination signal is reached.

• The RNA molecule is released and the double helix structure of the DNA is re-established.

Components Of Rna Polymerase

The components of RNA Polymerase are:

Bacteria

The core enzyme of bacterial RNA Polymerase has a composition of five subunits: two alpha subunits, one beta subunit, one beta prime subunit, and one omega subunit.

Alpha (α) Subunits: Assembly of the enzyme and contact with the regulatory proteins. Each α subunit is composed of two domains, an N-terminal domain, NTD, and a C-terminal domain, CTD. The latter, being CTD, can interact with DNA and transcription factors.

Beta and Beta Prime Subunits (β and β'): They form the catalytic centre wherein the RNA synthesis takes place. The β subunit is main for forming, in particular, the phosphodiester bonds between nucleotides. Meanwhile, the β' subunit also has a role in DNA binding.

Omega Subunit (ω): This provides stability to the whole RNA Polymerase complex and helps the assembly of its core enzyme.

Sigma Factor (σ)

The σ factor is required for initiation of transcription. This factor instructs RNA Polymerase which promoter sites to go to on the DNA and aids the enzyme in initiating synthesis at the correct location on the RNA.

Multiple σ factors exist in the bacteria, each recognizing different sets of promoters that enable the bacteria to distinguish between a broad range of environmental conditions and stresses.

Eukaryotes

Eukaryotic cells contain three main types of RNA Polymerase, each specialized to transcribe different classes of genes.

RNA Polymerase I: Transcribes most ribosomal RNA genes - in particular, 5.8S, 18S, and 28S rRNA. This enzyme is localised within the nucleolus.

Subunits: The enzyme consists of 14 subunits. Some of these represent eukaryotic homologues of bacterial RNA Polymerase subunits.

RNA Polymerase II: Transcribes messenger RNA, specialised for protein-encoding messages, and a few small nuclear RNAs. It is mainly involved in splicing.

Subunits: It contains 12 subunits. The largest subunit has a C-terminal domain at the end with repeating heptapeptide sequences at the end, which are phosphorylated and therefore play a significant role in transcriptional regulation.

RNA Polymerase III: Transcribes transfer RNA, 5S rRNA, and other small RNAs.

Subunits: It is composed of 17 subunits, some of which come only with Pol III, whereas others are shared with Pol I and Pol II.

Eukaryotic RNA Polymerases are far from simple and need many more ancillary factors to generate the initiation complex.

Archaea

Archaeal RNA Polymerase is similar to eukaryotic RNA Polymerase II rather than bacterial RNA Polymerase. It shows the evolutionary history of archaea that is separable from that of bacteria.

Subunits: Contains a lot of subunits (~12-13); most of them have homologs in the eukaryotic RNA Polymerase II. This includes the biggest subunit, Rpo1, which has a homolog to the biggest subunit of RNA Polymerase II, RPB1, and other subunits similar to RPB2, RPB3, etc.

Transcription Factors:

Unlike bacteria, archaea do not utilise a σ factor for initiation. They instead rely on eukaryotic TBP and TFB-like transcription factors that recognise and bind to the promoter regions.

TFB and TBP: These factors help recruit the RNA polymerase to the DNA and are hence essential for the assembly of the initiation complex of transcription in archaea.

RNA Polymerase And Disease

Another avenue through which extremely severe activities can arise is mutation of genes encoding subunits or other factors of RNA Polymerase; for instance, many disorders of neurodevelopment have been described due to mutation in the POLR3A-encoded subunit of RNA Polymerase III.

It is also implicated in many diseases, among which is cancer since overexpression or mutations in subunits of RNA Polymerase II are detected in many tumors and can cause aberrant gene expression. Moreover, in viral infections, the host's RNA Polymerase machinery can be hijacked to start the transcription of viral genes at the cost of normal cellular functions.

Investigation of mechanisms resulting in mutations in the RNA polymerase gene and its misregulation can result in useful information on underlying mechanisms of disease, which can then be exploited in the development of diagnostic markers and therapeutic targets. Drugs such as inhibitors specifically designed to block the activity of mutant or overactive RNA polymerase would shortly be applied in cancer cells.

Experimental Techniques To Study RNA Polymerase

ChIP is also utilised to probe RNA Polymerase–DNA interactions. By using special antibodies recognizing RNA Polymerase or other associated proteins, it becomes possible to find the parts of the DNA bound by them. This shall therefore unfold information on the patterns of transcriptional control.

RNA sequencing is enabled to have meticulous information about RNA transcripts in the cell, identifying the genes which, at any specific time, are getting actively transcribed by RNA Polymerase and the information showing the tertiary expression of genes under different conditions.

Gel electrophoresis is used to separate and analyze RNA molecules. It can be used for the assessment of quality and size of RNA transcripts produced by RNA Polymerase, and therefore in the investigation of transcriptional fidelity and processing.

These experimental techniques are critical for the understanding of the function and regulation of RNA polymerase. They allow researchers to dissect complicated interactions and processes related to this enzyme, thus generally enhancing knowledge about gene expression and its impact on health and disease.

Conclusion

RNA Polymerase is engaged in the transcription of genetic information from DNA to RNA and, therefore, plays a cardinal role in gene expression and regulation. While it is highly conserved concerning structure and function, it is still adapted to the specific needs of prokaryotic and eukaryotic organisms. RNA Polymerase is far from being a simple enzyme; it holds the key to understanding the mechanisms of many diseases and to the rational design of targeted therapies. We learn more about how this important enzyme of biology works and its function through advanced experimental techniques that go on to evolve.

Recommended video for "RNA Polymerase"