page_title: RNA polymerase
section_title: Elongation
hierarchical_section_title: RNA polymerase / Action / Elongation
caption_attribution_description: The process of transcript elongation facilitated by disassembly of nucleosomes.
context_page_description: In molecular biology, RNA polymerase, is an enzyme that synthesizes RNA from a DNA template.
  Using the enzyme helicase, RNAP locally opens the double-stranded DNA 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 for protein coding, i.e. messenger RNA; or non-coding. At least four functional types of RNA genes exist:
  transfer RNA — transfers specific amino acids to growing polypeptide chains at the ribosomal site of protein synthesis during translation;
  ribosomal RNA — incorporates into ribosomes;
  micro RNA — regulates gene activity; and,
context_section_description: The 17-bp transcriptional complex has an 8-bp DNA-RNA hybrid, that is, 8 base-pairs involve the RNA transcript bound to the DNA template strand.  As transcription progresses, ribonucleotides are added to the 3' end of the RNA transcript and the RNAP complex moves along the DNA. The characteristic elongation rates in prokaryotes and eukaryotes are about 10–100 nts/sec.
  Aspartyl (asp) residues in the RNAP will hold on to Mg²⁺ ions, which will, in turn, coordinate the phosphates of the ribonucleotides.  The first Mg²⁺ will hold on to the α-phosphate of the NTP to be added.  This allows the nucleophilic attack of the 3'OH from the RNA transcript, adding another NTP to the chain.  The second Mg²⁺ will hold on to the pyrophosphate of the NTP.  The overall reaction equation is:
  (NMP)ₙ + NTP → (NMP)ₙ₊₁ + PPᵢ
caption: RNA Polymerase II Transcription: the process of transcript elongation facilitated by disassembly of nucleosomes.
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