Prokaryotic and eukaryotic transcription

RNA polymerase complex (or holoenzyme) binding to a specific DNA sequence at the beginning of a gene, known as the promoter, is required for transcription to begin in all species. The activation of the RNA polymerase complex allows for the initiation of transcription, which is followed by the elongation of the transcriptional transcript. As a result, transcript elongation results in the clearing of the promoter, allowing the transcription process to begin all over once more. As a result, transcription can be controlled at two different levels: at the promoter level (cis regulation) and at the polymerase level (trans regulation) (trans regulation). These characteristics differ between bacteria and eukaryotes.

Transcription in prokaryptes

In bacteria, a single type of RNA polymerase is responsible for all transcriptional activities. There are four catalytic subunits and a single regulatory subunit, which is known as sigma, in this polymerase (s). It is interesting to note that several distinct sigma factors have been identified, and each of these is responsible for the transcription of a distinct set of genes. Due to this discriminatory nature of sigma factors, they are found in only one set of promoter sequences.

Bacterial sporulation in the species Bacillus subtilis provides an excellent illustration of the specialisation of sigma factors for different gene promoters. This bacterium can be found in two states: vegetative (growing) and sporulating (producing spores). During vegetative growth, genes involved in spore formation are not typically expressed in high levels. Surprisingly, the expression of a gene encoding a novel sigma factor results in the activation of the first genes required for sporulation. The subsequent expression of different sigma factors then activates new sets of genes that are required later in the sporulation process. These sigma factors only recognise the promoters of genes in their own group, not the promoters of genes in other groups as “seen” by other sigma factors. This straightforward illustration demonstrates how transcription can be modulated in both the cis and trans directions to cause changes in cell function. Accordingly, despite the fact that bacteria accomplish transcription of all genes using a single type of RNA polymerase, the use of different sigma factor subunits provides an additional level of control.

Transcription in eukaryotes

Unlike prokaryotic RNA polymerase, which can bind to a DNA template on its own, eukaryotic RNA polymerase requires the assistance of several other proteins, known as transcription factors, to first bind to the promoter region of a DNA template and then aid in the recruitment of the proper polymerase. RNA polymerase and the assembled transcription factors bind to the promoter and form a transcription pre-initiation complex, which is responsible for initiating transcription (PIC).

The TATA box, a short DNA sequence occurring 25-30 base pairs upstream of the transcriptional start site in eukaryotes, is the most thoroughly studied core promoter element in eukaryotes. TATA boxes are found in only around 10-15 percent of mammalian genes, with the remainder including other core promoter elements. However, the methods by which transcription is triggered at promoters containing TATA boxes have been thoroughly investigated.

A transcription factor known as TATA-binding protein (TBP), which is itself a subunit of another transcription factor known as Transcription Factor II D, recognises the TATA box as a core promoter element and recognises it as a binding site for it (TFIID). Several transcription factors and RNA polymerase come together in a series of phases surrounding the TATA box after TFIID binds to it through the TBP to create the pre-initiation complex, which is required for transcription to begin. In particular, one transcription factor, Transcription Factor II H (TFIIH), is involved in the separation of opposing strands of double-stranded DNA to provide access to a single-stranded DNA template by the RNA Polymerase enzyme. The pre-initiation complex, on the other hand, is solely responsible for a very low, or basal, rate of transcription. Other proteins, such as transcription activators and repressors, as well as any related coactivators or corepressors, are responsible for controlling the rate at which genes are expressed. Activator proteins enhance the rate of transcription, whereas repressor proteins reduce the rate of transcription, respectively.

Prokaryotic and eukaryotic transcription differences

Conclusion

A very important process in the reproduction and evolution of life on the planet is the transcription of genetic information.RNA polymerase complex (or holoenzyme) binding to a specific DNA sequence at the beginning of a gene, known as the promoter, is required for transcription to begin in all species.

In bacteria, a single type of RNA polymerase is responsible for all transcriptional activities. There are four catalytic subunits and a single regulatory subunit, which is known as sigma, in this polymerase (s).

In, transcription in eukaryotes is accomplished through the action of three different types of RNA polymerase (RNA pol I-III).