RNA polymerase

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RNA polymerase (RNAP) in action. It is building a messenger RNA molecule from a DNA helix. Part of the enzyme was made transparent so the RNA and DNA can be seen. The magnesium ion (yellow) is located at the enzyme active site

RNA polymerase (RNAP) is the enzyme which does transcription.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.[1]

With the help of some other molecules, it makes messenger RNA from a strand of a DNA. This is its main function, but it does various other things. Products of RNAP include:

  • Messenger RNA (mRNA). These are templates for the synthesis of proteins by ribosomes.
  • Non-coding RNA or "RNA genes". These are a broad class of genes that encode RNA which is not translated into protein. The most important RNA genes are transfer RNA (tRNA) and ribosomal RNA (rRNA), both of which are involved in the process of translation. However, since the late 1990s, many new RNA genes have been found, and thus RNA genes may play a much more significant role than previously thought.
    • Transfer RNA (tRNA)—transfers specific amino acids to growing polypeptide chains at the ribosomal site of protein synthesis during translation
    • Ribosomal RNA (rRNA)—a component of ribosomes
    • Micro RNA—regulates gene activity
    • Catalytic RNA (Ribozyme)—enzymatically active RNA molecules

In eukaryotes[change | change source]

Structure of eukaryotic RNA polymerase II (light blue) in complex with α-amanitin (red), a strong poison found in death cap mushrooms that targets this vital enzyme

Eukaryotes have various RNAPs in their nuclei, each to synthesis a type of RNA. All are similar and related to each other and to bacterial RNAP:

Eukaryotic chloroplasts have an RNAP very similar to bacterial RNAP ("plastid-encoded polymerase"). Eukaryotic chloroplasts also have a second, unrelated, RNAP.

Eukaryotic mitochondria contain an unrelated RNAP (member of the "single-subunit RNAP" protein family).

X-ray crystallography of DNA and RNA polymerases show that, other than having a Mg2+ ion at the catalytic site, they are virtually unrelated to each other. So the two classes of enzyme have arisen independently twice in the early evolution of cells. One line led to the modern DNA polymerases and reverse transcriptases. The other line led to all modern cellular RNA polymerases.

References[change | change source]

  1. Nobel Prize in Chemistry 2006
  2. Grummt I. (1999). "Regulation of mammalian ribosomal gene transcription by RNA polymerase I.". Prog Nucleic Acid Res Mol Biol. 62: 109–54. doi:10.1016/S0079-6603(08)60506-1. PMID 9932453.
  3. Lee Y. et al (2004). "MicroRNA genes are transcribed by RNA polymerase II". EMBO J. 23 (20): 4051–60. doi:10.1038/sj.emboj.7600385. PMC 524334. PMID 15372072.
  4. Willis IM. (1993). "RNA polymerase III. Genes, factors and transcriptional specificity". Eur J Biochem. 212 (1): 1–11. doi:10.1111/j.1432-1033.1993.tb17626.x. PMID 8444147.
  5. Herr A.J. et al (2005). "RNA polymerase IV directs silencing of endogenous DNA". Science 308 (5718): 118–20. doi:10.1126/science.1106910. PMID 15692015.
  6. Wierzbicki A.T. et al (2009). "RNA Polymerase V transcription guides ARGONAUTE4 to chromatin". Nat. Genet. 41 (5): 630–4. doi:10.1038/ng.365. PMC 2674513. PMID 19377477.