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In most prokaryotes, a single RNA polymerase species transcribes all types of RNA. RNA polymerase "core" from E. coli consists of five subunits: two alpha (α) subunits of 36 kDa, a beta (β) subunit of 150 kDa, a beta prime subunit (β′) of 155 kDa, and a small omega (ω) subunit. A sigma (σ) factor binds to the core, forming the holoenzyme.
RNA polymerase I. RNA polymerase 1 (also known as Pol I) is, in higher eukaryotes, the polymerase that only transcribes ribosomal RNA (but not 5S rRNA, which is synthesized by RNA polymerase III), a type of RNA that accounts for over 50% of the total RNA synthesized in a cell. [1]
Promoters can be about 100–1000 base pairs long, the sequence of which is highly dependent on the gene and product of transcription, type or class of RNA polymerase recruited to the site, and species of organism. [1][2] Promoters control gene expression in bacteria and eukaryotes. [3]
RNA polymerase II (RNAP II and Pol II) is a multiprotein complex that transcribes DNA into precursors of messenger RNA (mRNA) and most small nuclear RNA (snRNA) and microRNA. [1][2] It is one of the three RNAP enzymes found in the nucleus of eukaryotic cells. [3] A 550 kDa complex of 12 subunits, RNAP II is the most studied type of RNA polymerase.
RNA polymerase core enzyme binds to the bacterial general transcription (sigma) factor to form RNA polymerase holoenzyme and then binds to a promoter. [6] (RNA polymerase is called a holoenzyme when sigma subunit is attached to the core enzyme which is consist of 2 α subunits, 1 β subunit, 1 β' subunit only).
Sigma factor. A sigma factor (σ factor or specificity factor) is a protein needed for initiation of transcription in bacteria. [1][2] It is a bacterial transcription initiation factor that enables specific binding of RNA polymerase (RNAP) to gene promoters. It is homologous to archaeal transcription factor B and to eukaryotic factor TFIIB. [3]
A transcription factor is a protein that binds to specific DNA sequences (enhancer or promoter), either alone or with other proteins in a complex, to control the rate of transcription of genetic information from DNA to messenger RNA by promoting (serving as an activator) or blocking (serving as a repressor) the recruitment of RNA polymerase. [3 ...
The preinitiation complex (abbreviated PIC) is a complex of approximately 100 proteins that is necessary for the transcription of protein-coding genes in eukaryotes and archaea. The preinitiation complex positions RNA polymerase II (Pol II) at gene transcription start sites, denatures the DNA, and positions the DNA in the RNA polymerase II ...