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RNA polymerase

RNA polymerase (ribonucleic acid polymerase), abbreviated RNAP or RNApol, officially DNA-directed RNA polymerase, is an enzyme that synthesizes RNA from a DNA template. RNAP locally opens the double-stranded DNA (usually about four turns of the double helix) so that one strand of the exposed nucleotides can be used as a template for the synthesis of RNA, a process called transcription. A transcription factor and its associated transcription mediator complex must be attached to a DNA binding site called a promoter region before RNAP can initiate the DNA unwinding at that position. RNAP not only initiates RNA transcription, it also guides the nucleotides into position, facilitates attachment and elongation, has intrinsic proofreading and replacement capabilities, and termination recognition capability. In eukaryotes, RNAP can build chains as long as 2.4 million nucleotides. RNA polymerase (ribonucleic acid polymerase), abbreviated RNAP or RNApol, officially DNA-directed RNA polymerase, is an enzyme that synthesizes RNA from a DNA template. RNAP locally opens the double-stranded DNA (usually about four turns of the double helix) so that one strand of the exposed nucleotides can be used as a template for the synthesis of RNA, a process called transcription. A transcription factor and its associated transcription mediator complex must be attached to a DNA binding site called a promoter region before RNAP can initiate the DNA unwinding at that position. RNAP not only initiates RNA transcription, it also guides the nucleotides into position, facilitates attachment and elongation, has intrinsic proofreading and replacement capabilities, and termination recognition capability. In eukaryotes, RNAP can build chains as long as 2.4 million nucleotides. RNAP produces RNA that functionally is either coding (for protein) (messenger RNA) (mRNA); or non-coding: so-called 'RNA genes'. At least four functional types of RNA genes exist: RNA polymerase is essential to life, and is found in all living organisms and many viruses. Depending on the organism, a RNA polymerase can be a protein complex (multi-subunit RNAP) or only consist of one subunit (single-subunit SNAP, ssSNAP), each representing an independent lineage. The former is found in bacteria, archaea, and eukaryotes alike, sharing a similar core structure and mechanism. The latter is found in phages as well as eukaryotic chloroplasts and mitochondria, and is related to modern DNA polymerases. Eukaryotic and archaeal RNAPs have more subunits than bacterial ones do, and are controlled differently. Bacteria and archaea only have one RNA polymerase. Eukaryotes have multiple types of nuclear RNAP, each responsible for synthesis of a distinct subset of RNA. RNA polymerase I synthesizes a pre-rRNA 45S (35S in yeast), which matures and will form the major RNA sections of the ribosome. RNA polymerase II synthesizes precursors of mRNAs and most snRNA and microRNAs. RNA polymerase III synthesizes tRNAs, rRNA 5S and other small RNAs found in the nucleus and cytosol. RNA polymerase IV and V found in plants are less-understood; they make siRNA. In addition to the ssSNAPs, chloroplasts also encode and use a bacteria-like RNAP. The 2006 Nobel Prize in Chemistry was awarded to Roger D. Kornberg for creating detailed molecular images of RNA polymerase during various stages of the transcription process. 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. After transcription starts, the factor can unbind and let the core enzyme proceed with its work. The core RNA polymerase complex forms a 'crab claw' or 'clamp-jaw' structure with an internal channel running along the full length. Eukaryotic and archaeal RNA polymerases have a similar core structure and work in a similar manner, although they have many extra subunits. All RNAPs contain metal cofactors, in particular zinc and magnesium cations which aid in the transcription process. Control of the process of gene transcription affects patterns of gene expression and, thereby, allows a cell to adapt to a changing environment, perform specialized roles within an organism, and maintain basic metabolic processes necessary for survival. Therefore, it is hardly surprising that the activity of RNAP is long, complex, and highly regulated. In Escherichia coli bacteria, more than 100 transcription factors have been identified, which modify the activity of RNAP. RNAP can initiate transcription at specific DNA sequences known as promoters. It then produces an RNA chain, which is complementary to the template DNA strand. The process of adding nucleotides to the RNA strand is known as elongation; in eukaryotes, RNAP can build chains as long as 2.4 million nucleotides (the full length of the dystrophin gene). RNAP will preferentially release its RNA transcript at specific DNA sequences encoded at the end of genes, which are known as terminators.

[ "Transcription (biology)", "RNA", "Escherichia coli", "Sequivirus", "DnaG Gene Product", "RNA Polymerase Sigma 54", "DNA-Dependent RNA Polymerase I", "RNA polymerase alpha subunit" ]
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