Transcription (傳寫 or 轉寫, English: transcription) is the process of transferring genetic information written in DNA into mRNA. RNA polymerase is responsible for this process. Basically, it is similar to one part of the DNA replication process, but in the transcription process, only one strand is used as information and transferred, and after RNA is synthesized, the DNA is restored to its original state.
In the case of prokaryotic cells, the transcribed mRNA goes directly to the next process, the translation process, but in the case of eukaryotic cells, the intron in the middle is removed and only the exon is left, so the prepared mRNA is processed.
The production of RNA using one strand of DNA as a template is called DNA-dependent RNA polymerase, and transcription is performed by this enzyme.
Transcription in prokaryotes begins when RNA polymerase attaches to DNA. Since this enzyme synthesizes complementary RNA molecules using DNA as a template, it is called DNA-dependent RNA polymerase (DNA-dependent RNA ploymerase). In general, E. coli has about 7000 RNA polymerases, and this enzyme can select and bind nucleotides that are precisely complementary to the base sequence of the template, as well as find out where the gene to be transcribed is located. Transcription of prokaryotes starts by attaching RNA polymerase and a very small number of proteins to DNA together. At this time, other than RNA polymerase, the attached proteins act as mediators controlling subtle parts of transcription. However, the role of such a mediator in transcription in prokaryotes is minimal compared to that in eukaryotes.
Transcription in eukaryotes is very different from transcription in prokaryotes. The main difference is that transcription in eukaryotes involves several mediators other than RNA polymerase. Unlike prokaryotes, in eukaryotes, numerous proteins are needed to subtly control the degree of transcription, that is, the amount and speed of transcription, and the type of protein to be transcribed. These proteins are called transcription factors, and examples thereof include AP-1 and NF-κB.
As transcription factors and RNA polymerase form a complex step by step or all at once, it is determined with what strength to attach to a specific region of DNA. While transcription in prokaryotes is mostly regulated by direct binding between RNA polymerase and DNA, transcription in eukaryotes is regulated by binding of DNA with a complex of transcription factors and RNA polymerase. Therefore, transcription in eukaryotes is a process in which the role of a regulator called a transcription factor plays a decisive role, not simply the binding between RNA polymerase and DNA.
Beginning of the Warrior
DNA normally has a very dense structure with proteins called histones. As a result, transcription factors and RNA polymerase cannot access the DNA. That is, DNA exists in a form in which transcription cannot normally occur. In order for transcription to occur, an acetyl group (a hydroxyl group -OH removed from CH3COOH acetate) is attached to the histone, and the shape of the histone is changed and the structure of DNA is unraveled.
Several proteins are attached to the site where transcription will occur, and the DNA with the two strands attached to each other is slowly unwound. At this time, in order to suppress the process of spontaneously becoming two strands again, a specific protein (SSB, single-strand binding protein) is attached to the single-stranded DNA so that it continues to exist as one strand.
Progress of the Warrior
Elongation Using one of the two DNA strands as a template