RNA Polymerases

RNA Polymerases from Eukaryotic Organisms

There are three distinct nuclear RNA polymerases present in eukaryotic cells. These polymerases transcribe three distinct categories of genes. RNA polymerase II is responsible for the transcription of protein-coding genes, which results in the production of messenger RNAs (mRNAs). RNA polymerases I and III are responsible for the transcription of ribosomal RNAs and transfer RNAs, respectively. The transcription of the three largest species of rRNAs, which are designated as 28S, 18S and 5.8S according to their rates of sedimentation during velocity centrifugation, is the sole responsibility of RNA polymerase I. RNA polymerase III is responsible for the transcription of the genes that code for transfer RNAs as well as the smallest species of ribosomal RNA (5S rRNA). While some of the small RNAs (snRNAs and scRNAs) that are involved in protein transport and splicing are transcribed by RNA polymerase III, others are polymerase II transcripts. In addition, separate RNA polymerases that are analogous to bacterial RNA polymerases can be found in chloroplasts and mitochondria, and it is the function of these RNA polymerases to specifically transcribe the DNAs of those organelles.

Distinctions between the various forms of RNA polymerase

Eukaryotic organisms like plants and mammals can have many different types of RNA polymerase, in contrast to prokaryotic organisms like bacteria, which only have one RNA polymerase that can transcribe all types of RNA.

RNA polymerase I and RNA polymerase I are the enzymes that are in charge of synthesising the majority of the ribosomal RNA (rRNA) transcripts. These transcripts are manufactured in the nucleolus, which is a region found within the nucleus that is responsible for the assembly of ribosomes. Due to the fact that these transcripts are directly involved with the production of ribosomes, the availability of rRNA molecules that are produced by RNA polymerase can have an effect on essential functions of cell biology.

The RNA polymerase II enzyme

RNA polymerase II is responsible for the transcription of genes that code for proteins into messenger RNA (mRNA). Producing pre-mRNA transcripts allows this enzyme with 12 subunits to function as a complex that has a direct impact on gene expression. After RNA polymerase II in the nucleus has finished releasing the pre-mRNAs, biochemical modifications will be made to the transcripts in order to get them ready for translation. RNA polymerase II also produces micro RNA (miRNA) molecules. After transcription, these non-coding transcripts have the potential to mediate gene expression as well as the activity of mRNAs.

RNA genes are transcribed into small RNAs by RNA polymerase III and RNA polymerase III2, which include transfer RNA (tRNA) and 5S ribosomal RNA. Both the nucleus and the cytoplasm contribute to the normal functioning of the cell through the participation of these shorter RNA transcripts.

RNA polymerase IV and V are two types of transcription enzymes that can only be found in plants. These enzymes evolved from RNA polymerase II4 to become more specialised over the course of evolution. Both enzymes are responsible for the production of small interfering RNA (siRNA) transcripts, which are an important component in the process of gene silencing in plants.

RNA polymerase and various medications

Because it is present and performs its function throughout the entire life cycle, RNA polymerase makes an interesting target for the research and development of new drugs. Because of the distinct biochemical properties of RNA polymerase found in prokaryotes and eukaryotes, it is possible to develop drugs that specifically target microbial RNA polymerases without causing any interaction with our own.

A number of antimicrobial drugs can block the activity of bacterial or viral enzymes 

During one stage of transcription, allowing them to function as RNA polymerase inhibitors. For instance, elongation can be inhibited by blocking the exit channel of RNA polymerase using a class of antibiotics called rifamycins. Rifamycins are produced by bacteria. These medications are frequently employed in the treatment of difficult infections brought on by leprosy and tuberculosis.

Conclusion

RNA is produced by RNA polymerases, which catalyse reaction. The action of RNA polymerases is comparable to that of DNA polymerases, which are responsible for reaction. In reaction, the 5′-RNA-polymer-3′-H molecule represents the growing RNA chain, and the NTP molecule represents the ribonucleoside triphosphate. One of the products, known as 5′-RNA-polymer-NMP-3′-OH, is a reflection of the incorporation of ribonucleoside.