RNA Polymerase

Multiple subunits make up the RNA polymerase enzyme, which is a huge complex. The four subunits of bacterial RNA polymerase are capable of transcribing all forms of RNA. These enzymes have eight or more subunits in eukaryotes and help with the attachment and processing of DNA during transcription.

To do their activity, RNA polymerases interact with a variety of proteins. These proteins aid in improving the enzyme’s binding specificity, unwinding the double helix structure of DNA, modulating the enzyme’s activity based on the cell’s needs, and altering transcription speed. Some RNAP molecules can accelerate the production of a four-thousand-base-long polymer in less than a minute. They do, however, have a dynamic range of velocities and can halt or even stop at specific sequences to ensure integrity during transcription.

Transcription

One of the initial steps in gene expression is transcription. Genetic information is transferred from DNA to proteins via a transcription and translation process. The template strand is the only strand of DNA copied during transcription, and the RNA produced is known as mRNA.

Transcription’s primary goal is to create an RNA copy from a DNA sequence. The information used to code a protein is carried by the RNA transcript.

Stages of Transcription: The three phases of transcription entail different RNA polymerase actions that result in RNA synthesis:

• Initiation: – When RNA polymerase wraps around the promoter region of DNA, the process begins. The promoter is a DNA segment that instructs RNA polymerase on how to attach to a gene upstream. While bacterial RNA polymerase can directly attach to DNA promoter regions, transcription factors are required for first binding in eukaryotic forms. After successfully binding DNA at the specific promoter region, RNA polymerase can proceed to the second stage of transcription.
• Elongation RNA polymerase unwinds double-stranded DNA into two single strands, which starts the elongation process. The genetic templates for RNA production are these DNA strands. The RNA polymerase creates an RNA strand that complements the transcribed DNA strand as the DNA template strand passes through it.
• Termination is the last stage in the transcription process. RNA polymerase stops adding complementary nucleotides to the RNA strand when it comes across a terminator sequence or signal. Following that, the RNA transcript is released, signalling the end of transcription for that DNA template.

Different types of RNA Polymerases

The transcription procedure comes to a close with this step. When it encounters a terminator sequence or a signal, RNA polymerase stops adding complementary nucleotides to the RNA strand. The RNA transcript is then released, signalling that transcription for that DNA template has come to a stop.

RNA polymerase I

Most ribosomal RNA (rRNA) transcripts are synthesized by RNA polymerase I2. These transcripts are produced in the nucleolus, a part of the nucleus where ribosomes are constructed. Because these transcripts are directly associated with the creation of ribosomes, the availability of rRNA molecules synthesized by RNA polymerase can have an impact on the fundamental activities of cell biology.

RNA polymerase II

RNA polymerase II transcribes protein-coding genes into messenger RNA (mRNA). This 12-subunit enzyme acts as a complex that directly controls gene expression by synthesizing pre-mRNA transcripts. After RNA polymerase II releases pre-mRNAs into the nucleus, biochemical changes prepare them for translation. After transcription, these non-coding transcripts can regulate gene expression and mRNA activity.

RNA polymerase III

RNA polymerase III2 is responsible for converting rRNA genes into tiny RNAs such as transfer RNA (tRNA) and 5S rRNA. In the nucleus and cytoplasm, these smaller RNA transcripts play a role in regular cell function.

RNA polymerase IV and V

RNA polymerase IV and V are transcription enzymes that originated from specialized versions of RNA polymerase II4 and are only present in plants. Small interfering RNA (siRNA) transcripts are produced by both enzymes and play a role in the silencing of plant genes.

Requirement of RNA polymerase

The initial DNA-RNA heteroduplex is subsequently synthesized by RNA polymerase, with ribonucleotides base-paired to the template DNA strand according to Watson-Crick base-pairing interactions. As previously stated, RNA polymerase interacts with the promoter region. However, these stabilizing connections prevent the enzyme from accessing DNA farther downstream, preventing the full-length product from being synthesized. RNA polymerase must escape the promoter to continue RNA synthesis. It must retain promoter connections while unwinding and “scrunching” additional downstream DNA into the initiation complex for synthesis. Thermodynamically, stress is accumulated as a result of DNA unwinding and compaction. RNA polymerase releases its upstream connections and efficiently achieves the promoter escape transition into the elongation phase once the DNA-RNA heteroduplex is long enough (10 bp). The elongation complex is stabilized by the heteroduplex at the active centre.

However, promoter emigration isn’t the only possibility. The stress can potentially be relieved by RNA polymerase releasing its downstream connections, halting transcription. 

The halted transcribing complex has two options: 

1. release the nascent transcript and start over at the promoter, or 
2. employ RNA polymerase’s catalytic activity to reestablish a new 3′-OH on the nascent transcript at the active site and resume DNA scrunching to achieve promoter escape. 

Abortive transcription is caused by the unproductive cycling of RNA polymerase before the promoter escape transition, which results in small RNA fragments of roughly 9 bp. The presence of transcription factors and the intensity of promoter interactions determine the extent of abortive initiation. 

Functions of RNA polymerase

• The RNA molecule is a messenger molecule that is utilized to transport DNA-coded information out of the cell nucleus and to create proteins in the cytoplasm.
• RNA polymerase is a protein that is used to make a variety of compounds. One of its responsibilities is to control the number and type of RNA transcripts that are created in response to the cell’s needs.
• On the carboxyl-terminal, the RNA polymerase enzyme interacts with various molecular proteins, transcription factors, and signalling molecules, which govern its mechanisms, which play a key part in multicellular (eukaryotic) organisms gene expression and gene specialization.
• During the conversion of DNA to RNA, the RNA enzyme also ensures that there are no abnormalities or errors (transcription). An example, ensuring that the correct nucleotide is added to the freshly synthesized RNA strand, as well as inserting the appropriate amino acid base that is complementary to the DNA strand’s template.
• The RNA polymerase can then catalyze and extend the RNA strand while also proofreading the new strand and removing erroneous bases once the correct nucleotides have been introduced.
• RNA polymerase is also involved in the post-transcription modification of RNAs, transforming them into functional molecules that help molecules move from the nucleus to their target sites.

Conclusion

Ribonucleic Acid (RNA) polymerase is an enzyme that converts gene sequences into RNA-based genetic information that can be used in the production of proteins. We define RNA polymerase and investigate its numerous activities in cell biology in this article.