RNA polymerase IV

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RNA polymerase IV is an enzyme which synthesizes small interfering RNA (siRNA) in plants.[1][2] Polymerase IV is specific to plants genomes and is required for the synthesis of over 90% of 24-nt heterochromatic siRNA. [3]


RNA polymerase silences the transposons and repetitive DNA in the siRNA pathway.[1] The siRNA plays a major role in defending the genome against the invading viruses and transposable elements by RNA directed DNA methylation. [3]

Polymerase IV and ROS1 demethylase unlocks and recondenses the 5S rDNA chromatin, which is present in seed and used for the development of adult features in plants. [4] Polymerase IV is involved in setting the methylation patterns in the 5S genes during plant maturation.[4]

In arabidopsis, polymerase IV is known to interact with an RNA-dependent RNA polymerase, RDR2 and the collective activity of Pol IV-RDR2 is thought to give rise to the short dsRNAs which can be diced in to 24 nt siRNAs by DCL3.[1] [5]


  1. ^ a b c Herr AJ, Jensen MB, Dalmay T, Baulcombe DC (April 2005). "RNA polymerase IV directs silencing of endogenous DNA". Science. 308 (5718): 118–20. doi:10.1126/science.1106910. PMID 15692015.
  2. ^ Onodera Y, Haag JR, Ream T, Costa Nunes P, Pontes O, Pikaard CS (March 2005). "Plant nuclear RNA polymerase IV mediates siRNA and DNA methylation-dependent heterochromatin formation". Cell. 120 (5): 613–22. doi:10.1016/j.cell.2005.02.007. PMID 15766525.
  3. ^ a b Zhang X, Henderson IR, Lu C, Green PJ, Jacobsen SE (March 2007). "Role of RNA polymerase IV in plant small RNA metabolism". Proceedings of the National Academy of Sciences of the United States of America. 104 (11): 4536–41. doi:10.1073/pnas.0611456104. PMC 1810338. PMID 17360559.
  4. ^ a b Douet J, Blanchard B, Cuvillier C, Tourmente S (December 2008). "Interplay of RNA Pol IV and ROS1 during post-embryonic 5S rDNA chromatin remodeling". Plant & Cell Physiology. 49 (12): 1783–91. doi:10.1093/pcp/pcn152. PMID 18845569.
  5. ^ Haag JR, Ream TS, Marasco M, Nicora CD, Norbeck AD, Pasa-Tolic L, Pikaard CS (December 2012). "In vitro transcription activities of Pol IV, Pol V, and RDR2 reveal coupling of Pol IV and RDR2 for dsRNA synthesis in plant RNA silencing". Molecular Cell. 48 (5): 811–8. doi:10.1016/j.molcel.2012.09.027. PMC 3532817. PMID 23142082.